ranking guideline

All your answer are in this SEOmoz post by Rand Fishkin,

Perfecting Keyword Targeting & On-Page Optimization for SEO | SEOmoz

Yes.


But this is not applicable for all keywords (high competition.. etc)

Yes very possible. We may not exactly know how but Google has ways of picking out keywords to rank for within the content- optimized or not.

I can say that it will take a lot of efforts to rank a page without the keyword and also it will be possible for very low competition keywords.

On page keyword usage is just one component of Google’s ranking algorithm, so this is actually possible to focus on other aspects of optimization to improve your position in the search rankings, apart from using keywords in the content.

However, the question is why to rank a website for the keywords that are not in the site’s content? To me it sounds kind of misleading, because if people visit your site due to a particular keyword they typed in and then come to see the information different from they’d expect to find - the bounce rate of your site will be very high.

But actually, if you use the keyword in ALT texts behind images, or in the URL, I mean not exactly in the content but in other on-page elements, this will help you to rank for the keyword missing from the content. Another option is to use your linking profile - use the keyword in the anchor texts of inbound links to your site.

Also, there is such thing as Latent Semantic Indexing which allows Google to determine what a page is about and thus show it in search results even though the match is not exact. You can enter ‘~your keyword’ in Google search box and get the idea of relevant terms you may use to get ranked.