Hi,
First off Google loves fresh, relevant and authoritative content. That's the first thing you need to be getting right. Write for users first, search engines second. That said, there are important things you do need to consider when coding your site.
1. Your title tags need to be descriptive of your content. In terms of keywords, yes it's a good idea to have your main keyword phrase in there but it's more important that the title of the web page clearly describes the content on that page.
2. Descriptions, i.e. meta descriptions, need to also be descriptive of the content of the page. Again, you can place keywords in the description but make sure you don't stuff the description with keywords and also that the user can understand it. Keep them down to 160 characters or less.
3. Make sure your document is semantic. That simply means that each element best describes the data that is being presented. HTML5 can help even more with this.
4. Valid code helps too, as long as it isn't to the detriment of the user experience.
5. Make sure you have a consistent and well structured heading hirarachy. h1 then h2 then h3 and so on. Again, HTML5 can help organise this even better than previously with HTML 4.01.
6. Having the important content display first in the document is a good practice. Concerning WordPress, as long as you code your own theme or you use a well coded theme you can achieve this no problem.
7. Make sure your content is easily accessible. It is a good idea to make your website responsive too, so that all users on different types of devices can access your content. Navigation is important for content accessibility. Your internal linking structure can help you rank higher.
These are just a few basic pointers but there are many more and things change all the time.
Hope this helps.

Oh, and in answer to your question WordPress is really good for SEO.