I have only a few words (~15) per every page on my site. So AdSense has difficulties to supply a good, relevant ads. Can I influence on the process how AdSense selects the ads in some other way? May be I can suggest my own keywords or something else?
Having only 15 words on every page of your site could get your adsense account banned. You need to have more content.
Actually there is content but it is numbers, specials codes and almost without common words. I'm with AdSense more than year without problems. The only problem is stupid links that AdSense suggests. Ussually only one link from 4 is relevant, good link.
Use more content. It's just a crawler they use on the page to determine the targeting. If the targeting is off, you need more content. Also make use of head tags (h1, h2), and meta info as they do take that into account as well. Page titles, etc. Basic on page seo.
I have found the way how to influence on keywords AdSense selects. This article describes it: w w w.google.com/adsense/support/bin/answer.py?hl=en&answer=23168
No, not quite. The method you have above assumes that you have some good content to place in between those tags in the first place. If you just stick keywords in there, you're going to be looking at the business end of a ban.