Do I want to be a model
Despite the glamour and hype you have seen about the modeling profession, it's hard work. It's boring (sometimes) and it can be tedious. Prepared to be constantly rejected, get ready for some major ups and downs. Modelling is a lifestyle, not an 9-5 job. Not all jobs pay well. Unless you are seriously committed about modeling, willing to work at it on your own time, live a healthy life style, etc., you will not succeed as a model.
You have to understand that there are lots of other people who want to be models, it's a very competitive business. Are you willing to put the time and energy into competing with pretty much everyone you meet, 24 hrs a day?

Where do I start
You'll need a modeling portfolio, I'm sure you'll all know what one of those is but for those that don't it's basically a selection of pictures showing yourself in different outfits and poses. The standard size for the photos is 9 by 12 inches and you'll need around 10 - 12 photos. Make sure you focus on quality rather than quantity, remember, you're only as good as your worst photo. Make sure your portfolio has a selection of both head shots and full body shots. Make sure you get a variety of different looks such as swimwear, catalogue and lingerie, you get the idea, also get a couple of black and white shots in there. Avoid using pictures of the same shot.

It can be very advantageous to have photographs from different photographers in a portfolio. This will show the versatility in terms of styles and it will prove that a model can work with a variety of different people. Obviously, the cost of hiring different photographers for a portfolio is prohibitive, but there are many excellent photographers out there who will do prints for time - and of course many more bad ones. If you research what's on offer well, it can be an excellent alternative.
Before going ahead with a photo session ask to look at the photographers portfolio to see if you like his style of photography. No doubt if you go to the photographers studio to book the appointment he will have examples of his work on display anyway. If you've never done modelling before this will also be an excellent practice run for you. Avoid photographers wanting to take nude shots, if possible take a friend with you to the shoot.

The Comp Card
You'll definately need one of these. A comp card is what your modelling agency will use to market you.
What is a comp card? A composite card (sometimes called a ZED) is a model's business card. In most cases, your comp card is your one and only opportunity to make a good first impression. With that in mind it is important that the images on your card are your absolute best and nothing less. Additionally, the printing and reproduction quality is extremely important. Poor reproduction makes your images look bad and as a result - makes you look bad. Besides a great head-shot, the comp card will have other photos that show your experience, your versatility, range, and what type of work you are seeking. For best results all of the photos should be the highest quality you can obtain at your stage in your modeling career. Make sure the you have them printed on rigid card that will withstand a bit of wear and tear.

Be careful! Do NOT have a modeling agency print your comp card. If you do - they will put their logo on it. You are going to want to sign with as many agencies as possible if you are serious about getting work. Comp card printing can get expensive - print them yourself and give each agency copies - they have stickers that they can put on them with their contact information and you will save money.

The Agency
An agency or co-ordinator should represent models. The model must have a portfolio, and comp cards. The agency/coordinator provides you with work (That is their main purpose. It is safe to say that they work for you!) They make a commission on your fee.

GOLDEN RULE - Don't go with an agency who asks for money up front! You'll probably never hear from them again and I ceratainly doubt you'll ever get any work from them.

Also check to see if they are reputable and genuine. The agency/coordinator provides you with a safe working environment and looks after legalities of the paper work for the job. They provide their clients with "Professional" models. Keep copies of all-important papers, such as contracts etc. You may need these if you have a dispute with the agency/coordinator. It is wise to choose the agency/coordinator carefully so you can stay with that them.