As a SEO you hear this question often. As a regular webtrepreneur you ask it often. Today I’ll give you the most important answer.
You need to optimise… everything. It’s not enough to optimise the landing page (home, start or index page). When you don not optimise the “inner” pages, chances are that these land in the supplemental results of the search engines, costing your site a lot in terms of traffic and revenue.
The optimisation is not a random process. It has a lot to do with the topic of each page, the relevant keywords for that topic, a good link structure, unique text and content format, creativity and interactivity, URL names, on page optimisation and so on.
The amount of DIY SEO articles (some pretty good) stating that anyone could do the job of a SEO it is often misleading. The truth is that SEO is far from being easy. There are some easy SEO aspects (I’d call them common sense), but there are also the technical issues that need an “expert” touch for proper results.
In my opinion, SEO is a collaborative effort involving both the SEO expert and the website owner. No matter how skilled a SEO is, without full support from the website owner, he/she cannot go too far. So if you really need to know what to optimise, here is the real answer: optimise the teamwork between you and the SEO (expert or company) you choose for your site.