I am certainly not a SEO expert. Neverthless, I am developing web sites and I have to be able to deliver after all a SEO optimized web site.
Check your site using SEO Site Checkup, which will be able to report you how your site is doing in terms of SEO best practices. Try to keep your total score above 80%-90%.
Use a tool in order to monitor how you are doing on Page Rank and try to find patterns that works for you or even the patterns that is damaging your image and eliminate them.
Of course, the SEO success is a result that depends on a lot of factors and it's certainly not an one man show. At the end, there is not really an excuse for a Web Developer to not be able to deliver a finest SEO optimized web site.