How to Join AdSense
After you have created your website, click the button on the right to join. Most sites are either accepted or rejected within 24 to 48 hours, so you shouldn't have to wait too long to find out if your application has been approved.
Once you've been accepted, simply copy and paste the provided HTML code into any page that you'd like to show the ads. If you've done a good job of defining the content on your web pages, the ads that show should be relevant to the content of your page...increasing the chances of click-thrus by your visitors.
You can either display the ads vertically along side the page like Google does or in a banner-like formation horizontally across your pages. The placement is up to you. You can even customize the colors to match your site's theme.
If Your Site Is Rejected by Google...
If you receive that email from Google stating that your site has not been accepted, the first thing you should remember is that as an AdSense member, you become a partner and are representing Google, Inc.
They have to make sure the websites that display these ads are up to par or they could run the risk of losing advertisers. Imagine if you were paying Google to display your ad and you found it showing up on a poorly developed, junky website.
Of course, if your site is rejected, it doesn't mean it is poorly developed. There may be other reasons:
1) Is your site an "About Me" page?
Google does not usually accept these kinds of personal sites because most of them do not have a specific topic or theme. They are usually just random facts about the website owner or their hobbies, pictures, etc.
It would be difficult for Google's technology to display targeted ads on these kinds of pages because the topics vary from subject to subject.
They are looking for "themed" sites that contain a generous amount of information on a specific topic. It could be anything from sewing tips to sports. Just make sure there is an obvious theme with adequate information.
2) Is your site organized?
Be sure your site has a neat and clean navigation that's easy to follow. Also ensure all the links work and that there are no typos. Keep the colors to a minimum and make sure each page has a consistent layout.
3) How many pages are on your site?
Even though Google doesn't specify a page number requirement, many believe they are looking for web sites with a certain amount of content. Again, it's not likely a two-page site will get accepted. Try to strive for at least 15 pages.
4) Is your content solid?
Don't just submit a website with a bunch of links to other sites. Be sure you have a themed/niche site with enough original content of your own.
5) Is your site an exact carbon copy of someone else's?