If I had to pick a single efficient and affordable way of getting in front of a targeted audience I would have to recommend Facebook in-stream ads. You control the budget, the target group and the message and they are, right now, offering the highest conversion rates for mobile apps. Keep in mind that your app needs to be amazing - that's the most effective strategy of all...

Are you able to say who your audience is? Marketing a game vs a travel app vs a productivity app will require very different plans.

Besides the iTunes store, there are websites that list and review iPhone apps. I know http://bestreviewapp.com/ is one of them. People have to download your app before reviewing it.

I have other marketing strategies for apps, so if you are interested, I would be glad to schedule a call and share them with you.

Bruce

Sorry, no answer without more details.
However, some food for thought:
1) cost efficient depends where you revenue comes from.
2) exposure ≠ downloads
3) depends on product & demographic.

Create a portfolio of free similar audience apps that cross promote each other. You need traction with at least one app for this to work.

Simply put, the most cost-efficient way to get exposure and downloads for your iPhone app is by building a great viral loop into your product. Regardless of your audience or interaction, there is some kind of growth-loop available to you that by doing well, is going to be far more cost-effective than any of the other answers provided so far.

Paid acquisition, PR, really anything other than WOM (almost impossible to come by) or virality (which should be possible if your core audience cares about what you're doing) are going to be cost-inefficient relative to the competition for attention you're fighting against.

I'm happy to look at your product and in a quick call brainstorm some potential growth loops with you.

Agree with Tom here that the viral loop is crucial (as well as "simply" having a great product). But a big problem is getting that initial traction! And then a bigger problem is reaching a critical mass.

So how do you start that snowball?
What worked for me in the past, and is also working for startups I advise to today - is the development of automated tools that will reach out to your target audience. The market/industry is irrelevant, as long as you can identify where online your target audience is active, and then build tools around these websites/platforms.

The best case I can give you is SweetIM, where I was the second guy (Growth Hacker and Product Manager). When I joined we had a product in development and 0 users. When I left we had over 100M users and millions in revenue (check out TechCrunch story about it: http://techcrunch.com/2012/11/08/holy-emoticons-batman-perion-network-acquires-sweetpacks-for-41m/)

I've developed automated zero-cost user acquisition tools that worked and generated massive amount of users. Today I'm using the same techniques in order to generate traffic and installs for my current startup, as well as other startups I advise to.

In general I can say that you need to think outside the box! Otherwise how would your app stand out from the millions of apps out there?
Not sure what stage you're at, but Ideally you will have someone in your team that has a solid background in Product Management, Marketing, Computer Science, and a deep understanding in user-behavior / cognitive science. A person that will find the best way to reach out to potential users, he/she will know how to form habits among users, what will make them keep using the product, and what will make them invite the rest of the world!

Hi there, before increase your app visibility, you should optimize the following aspects to increase the download rates:
· App title - Make sure your app title unique and attractive.
· App icon - A better icon can increase your downloads up to 560%. keep your design simple and eye-catchy.
· Screenshots - Show off the best features of your app in the first two images. According to research by Storemaven 60% users won’t swipe past the first two screenshots.
· Description - To capture a user’s attention and keep longer utilization, your app description has to be precise and make the right direction attract users. So make sure to highlight your app features and advantages in the first line.
Get positive app reviews(http://www.reviewapp4u.com/?from=cr-chris ) - 95% users will take the app reviews as one of the most important reference factors to judge the app, and most people prefer to download an app which has much more positive reviews. With great reviews, your app is going to be in great shape to rack up downloads and beating out the competition.

Then you can increase your app visibility with the following methods:

Apply for Awards
Participating in app awards is the most recommended channel and I would highly suggest you take advantage of it. It can give you tons of press, exposure, reviews and plenty of downloads.These are many famous app awards sites, such as Appy Awards, Best App Ever Awards, AppCircus competition, Apple Design Awards, etc.

Get featured on App Store
According to App Annie’s Report a feature for a game can lead to a 140% increase in downloads and for non-games to a 25% increase. Apps which with the following features tend to be get featured :
· Great app
· Universal app
· The user experience should be top notch.
· With compelling product page: video, screenshots, a good name, and a quality description.
· Have good App Store Optimization(ASO): app name, keywords, and category.
· New apps and apps with significant updates

Cooperate with influencers
Most people like to follow others and be influenced by the words of some celebrities or well-known business people - having high-profile Facebook pages with 100,000+Likes mentioning your app is a huge win. Reach out to organizations whose goals align with yours, and give them a compelling reason to mention or link to your app on their page.

Hope those methods are useful to you.

Look some good marketplace beside apple store and choose some attractive and catchy name for your app to attract your target customers and then grab your social handles especially facebook twitter and snapchat and post links to your app alongwith some unique description. Tag your app correctly to your social links and make use of your own social connections to enhance the outreach of your app.

You can also offer some free beta downloads to get some initial reviews for your app and as a next step you can offer these free downloads to some tech blog writers who can write a blog on your app that will not only establish the credibility of your app but will be helpful in rapidly promoting your app.

You can use google analytics to measure the analytics of your app.

You can use the following ways to increase your iPhone App download:
1. Prioritize app store optimization: App Store Optimization (ASO) is a simple but crucial way to influence app downloads. Keep in mind that it requires a sustained effort to be successful. While app store rankings depend on metadata like keywords, description, ratings, and reviews there’s more to ASO than that. You also need to consider how keywords rank in each app category. For instance, casual games are most competitive for keywords, while music and trivia games are much easier to rank for. You can also perform A/B tests to see which store assets most resonate with your audience so you can continue refining your app store page.
2. Encourage user reviews: Raising your app store visibility is only one part of improving downloads. Once users find your app, you will need to convince them that your app is valuable and reliable enough to download. This is where reviews come in handy. As Nielsen’s Global Trust in Advertising Survey found, users tend to trust word-of-mouth recommendations, such as user reviews, over other forms of advertising. You can encourage user reviews through in-app messages, although you will need to be careful not to send too many notifications as that may end up alienating your audience. Reviews not only indicate the quality and relevance of your app to potential downloaders, but they also provide an excellent opportunity for you to engage with customers. If reviewers provide suggestions or even complaints, you can respond and show potential users how responsive you are to feedback. By doing this on a regular basis, you will inspire trust and encourage more app downloads as a result.
3. Ensure your app is crash-free: If your users find any problems with your app, they will share their grievances online so you can easily learn if your app is faulty. After you respond to their complaints, your developers should fix the problem immediately, so your app never crashes again. However, it’s more effective to take a proactive approach your app should undergo vigorous testing so that your developers can identify all potential bugs and resolve them before you make your app available to the public.
4. Motivate users to make referrals: Referrals are another way to demonstrate quality, relevance, and trust, which will help increase downloads. You can turn your existing users into brand ambassadors by giving them an incentive to refer your app to their friends. For example, if you have a cloud storage app, you can offer a free gig of storage if users refer your app to others. Or for a ride-sharing app, you can provide free ride credits in exchange for a referral.
5. Invest in content: Creating compelling and relevant content to promote your app can help you reach more potential users. It may be in the form of online articles, sponsored content, videos, or infographics, although it depends on your audience’s consumption habits. For a gaming app, you can produce walkthrough videos to show off your product’s rich visuals and gameplay to impress your audience. You can also share user-generated content to help build a sense of community.
6. Engage on social media: Content powers social media and maintaining a strong online presence can be an effective way to expand your reach and introduce your app to new customers. However, your target audience will spend time on one platform over another, so paying attention to your user demographics is crucial. Keep in mind that you will need to do more than share sale pitches on social media, to draw interest. Responding to your followers and asking them to share their thoughts demonstrates that you care about your audience’s opinions.
7. Influencer and community outreach: Influencers have the power to affect the purchasing designs of your target audience. Reviews from recognized experts not only bring more exposure to your app, but they also instil more trust in your product. By researching the right influencers for your community, you can establish a beneficial partnership that will build your brand and boost app downloads.
8. Measure, analyse, optimize: Of course, it’s important to constantly analyse how users are interacting with your app in order to ensure that they remain engaged. Are they successfully using the app the way it was meant to be used? Are there any roadblocks that are preventing you from monetizing your app? You can use these insights to optimize your future campaigns. Perhaps you have noticed that many users from a certain source stop interacting with your app after a day or two. That may be because they were not a qualified audience, so you can choose to re-direct your campaign efforts to other acquisition sources.
9. Put your mobile-best foot forward: App stores are only becoming more saturated, and with the industry moving toward the convergence of mobile web and mobile apps, it’s wise to consider how your brand translates across multiple channels instead of focusing on just your app (or just your web) experience. Of course, it is more than just marketing across those channels, but being able to measure their effectiveness too.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath