Don't put ads on empty pages.
When I reworked my site, I built a skeleton set of pages that had no content, just titles and some meta tags. I displayed ads on those pages, however. Although all you see are public service ads at first, the very act of displaying ads on a page causes the AdSense web crawler to quickly fetch that page for analysis. A page with good content will thus begin showing relevant paying ads fairly quickly.
If you don't have any content, then, Google will have to guess as what your page is about. It may guess wrong, and so the ads that it displays may not be relevant. You'll have to wait until Google re-crawls the site for the ads to correct themselves. Here is what Google had to say when I asked them about how often the AdSense crawler updates a site
Check your keyword density
Although Google doesn't release exact details as to how they determine the ads to serve on a given page, they do tell us that it's the text content of the page that matters, not the meta tags. Before serving ads on a page, then, you might want to check its keyword density. A good, free tool for doing this is found here: