After extensive and expensive research I can exclusively reveal the secrets of Adsense.
The secret is it makes Google a lot of money.
It also seems to make some "internet marketeers" a fair wodge but after carefully reviewing their proposals it all comes down to getting people to click on adverts on your web page. Your chances of getting people to your web page in the first place are small to the point of non existence and the chances of a click on the ads once they get there even less so.
If you want to make some money go and get a job. Just don't build your hopes on the Internet and all those Get Rich Quick schemes. They don't work except of course for the authors.
Now I'm not saying that it doesn't work. Adwords, where you pay for keywords, are effective (ish). The secret is that you must appear at the top of the page or it's a complete waste of time. It's just another form of advertising and costs us around £40 per week. From this we might get a couple of sales per month.
As for Adsense, the number of clicks we get is pathetic. We have tried running ads for potentially useful information but it wouldn't pay for a pint.
I'm sure some people get lucky, but you probably won't be one of them.