Content optimization is about producing content that your audience find valuable. You can start with optimizing existing page content rather than focusing on producing new content on your blog. Here, optimize titles, descriptions, headings and messaging for topical/keyword focus.

You can also look at the architectural issues of your site such as spiderability, broken links, navigational issues, etc. These can all get you some tracking with rankings when focused correctly.

Internal blogs do provide you with good regular internal linking to your key products or service landing pages, which in turn can help you to increase organic visibility on the search engine results for your key target terms.

However if you do not have the resource to do this more advanced strategy then you need to get your on-page setup of you core target landing pages very well optimized.

Key on-page elements:
Meta Title Optimisation:
- Create Unique Titles for Each Page
- Embed Long Tail Keywords In Title Tags
- Optimize Your Meta Description for CTR

Content:
- Include engaging media formats on your landing pages
- Include Keyword Synonyms in H1 and H2 Tags
- Include high text frequency on your pages (1000 word +)
- Use concise keyword focused URLS
- Focus on keyword frequency in your landing page content with related keyword synonyms included

These types of recommendations are presented very well by Moz in the example landing page graphics at https://moz.com/blog/visual-guide-to-keyword-targeting-onpage-optimization and also Backlinko.com has just put together a very good list of SEO tactics to implement on your site that includes a list sorted into an on-page section at http://backlinko.com/actionable-seo-tips

On-page optimisation is an absolute must at the bottom of the SEO strategy pyramid however to compete on some very competitive terms with a number of bigger websites and brands it can be much harder to compete if you don't have a content marketing strategy to support your SEO strategy as often this can result in gaining external links that can be the key differentiator in whether you rank higher than your competitors on average.

Hope this helps.