So here are a bunch of tips that come handy under every amateur or professional optimizer's belt.
The first thing you need to take care of is the actual source code and layout of your page. This has to be kept as simple as possible. The problem comes when AdSense and the search engines themselves begin to have troubles in extracting the most relevant keywords on your site because of a too complex layout.
Secondly, try to have each one of your pages target only one specific topic. This way it is a lot easier for them to get indexed properly and for the AdSense ads to be consistent with the content of the site itself. Also, try not to include too many hyperlinks in your page as well. This also means you should try not to use too many AdSense ads on your page either. If there are certain keywords you wish to target, make sure the word you wish to target is present in the title, in the first paragraphs as well as in the name of the file. While you're at it you might want to ensure the word springs up in the page's last paragraphs. And of course, it's very important for your content to have original and compelling content.
How do you do this? Well the easiest way to do it is to find something you're really passionate about. That way, providing you give it a lot of effort you're bound to have a great page quite fast. If the content you use in your site is in the public domain (which is highly discouraged) make sure that you at least give it an original title, and add an opening and a closing paragraph of your own. This takes a little while, but if, after waiting, you still can't find your page near the top, you should try rewriting your title and your first and last paragraphs. It doesn't take much, often just changing a few words will give you the right results. And of, course there's the use of keyword tools that may aid you in finding some good keywords to include on your page that will drive visitors to your site more and more.
So those are about the basic techniques in search engine optimization. You can find a lot of computer tools to aid you in doing this, and of course, Google is a great place to search for this. In the end, you'll find that SEO is a complex topic, and entire books have been written on the topic as well. You might find that you have a lot of optimization you need to do in order to get more and more visitors to your site and clicking those precious AdSense banners.