Like fearless leader said, word of mouth is the best advertising.
Here at school, I went out one Sunday afternoon to take pictures of some of the guys in my house skateboard. After, I showed them the pictures, and since I'm a nice guy gave them the pictures for free.
Anyways, long story short, they started telling everybody that I was a good photographer (which is crap, but I'll take what they give me). I then started taking pictures for the rugby team, for other peoples school projects, and even for facebook profiles.
Now I need to know how to make some money off of it
So, if any of your friends do something, like mountain biking, skateboarding, etc... It would be a good idea to go and take pictures of them. You will learn alot, and it will get the word of mouth out there.