Google AdSense is a great way to earn some quick cash.
If you have a blog or other website with original content that you're willing to update with your own fresh ideas, then you'll want to include Google AdSense. But before you do, it's important to verify that your page is ready to accept Google AdSense and make the most profit.
Google AdSense will scan your website, and based on the content and keywords it finds there, it will target advertisements based on that content. Therefore, if you have a blog entry with a bunch of keywords that don't really have much to do with the overall content of your website, you're going to have advertisements that aren't really going to target your audience, and therefore aren't going to bring you any profit.
The point is that you shouldn't rush to include Google AdSense on your website just to start making money sooner. In the long run, you're going to make a lot more money using AdSense if you wait until you've developed a solid website with a good amount of solid content. That way, when AdSense scans your page, it's going to come up with advertisements targeted at your audience... and that's money in the bank!