OK, so it's not that easy

But one way of doing it if you have no site of your own is to use a descent online resource that pays you a share of the advertising revenue on that page and Hubpages is one such place, I have a page here, and will eventually add more.

You need an account with Kontera (like Infolinks), Google, Adsense and Amazon to get the best out of it, and don't expect a glut of money, especially if you include articles on crap. By that I mean cheap keywords, especially longtails (a phrase of 3 or more words).

Cheap Flights To Las Vegas is a 5 word longtail keyword. And as it is travel relevant the keywords are worth average. You then include the longtail in your title, and article about 3-5 times. This then helps it be discovered on the search engines easier when people search for the longtail.

You can find longtails at Wordtracker and Adsense, you get the value as well on the latter. You are looking for ones of decent value $1+, and competion no more than 50%, but over 1000 searches.

You need to publish new pages on a regular basis to stand any chance of making a few extra quid a month.