How do I start making money out of the ads I place on my web page?

If we take Google ads for an example, you won’t make money from placing them on your page unless visitors are clicking them. So even if there are thousands of people visiting your web site everyday, you won’t make money at all unless a great number of these visitors click on those ads.

So, can somebody give me an advice on how to (legally) get as many visitors as possible to click on my ads?