Hi :) I've been a model for 4 years now. I have to say, it is hard to make any money, if you want to do fashion/fitness and so on. It took me two years, where I had to do a lot of free shoots, to build up my portfolio. I make money on it now, but it has taken alot of work, so you need to be determined.
I would suggest that you find photographers in your reach, that you like. Send them an email, saying that you wish to build up a portfolio, and that you would like to do it like TFP (nobody pays eachother, you both get pictures for your port) Then when you have some pictures, you can start contacting agencies, if you want. If you want to do it without any agencies, then upload your port to modelmayhem.com deviantart.com and facebook. Facebook has groups for models and photographers, and I myself have gotten quit a few gigs via facebook.
I do have to say, if you want to make money fast in the industry, it is most likely not going to be in fashion or fitness, but in babe/nude, and its important never to be tempted to do that, if you dont really want to. Also remember, when the pics are out (regardless of style) they will never go away. You have to decide if you want your pictures all over the internet. I know it doesnt seem like a hard thing, if you are not doing nudes, but when my fashion pictures started sky rocking, I found myself alittle overwhelmed.
One other important thing, practice. Practice in front of your mirror, doing poses and different faceial exspressions, because the photographer & possible co-models, will most likely not want to work with you again, if they have to pull it out of you.
I hope I havent scared you of or anything, But I know the industry, and I think its best to just be honest. If its the money thats driving and not so much the pictures, then theres a great chance, you'll get disappointed, because those first years, are rough.