I found this blog post on Ancilla Tilia's DeviantArt blog.
It's too big to post here and it also wouldn't be fair to her as I think she deserves all the credit here.
I'm pasting a small excerpt from the beginning and you can find the links to the whole post below.

REALLY REALLY GOOD!

So here's from Ancilla:

I posted this on my forum (www.AncillaTilia.com/forum) quite a while ago to answer a question a girl posted on there.

I still get this question quite a lot so I figured it'd be better to answer this publically where everyone can read. Ofcourse there are so many things to keep in mind that will apply to every individual who's thinking about modelling, but I will keep it simple and start with the basics...

Do you have pictures? You will need some. They don't need to be great, but you need to be able to show photographers you want to work with what you look like. In the beginning you will not want to get paid for shoots because you are a starting model and you will want to work with good people who you should be honored with to work with without paying them. (generally called "TFCD"- Time For CD, with all your pics on a disc or "TFP"- time for print- and less usefull in this digital era)
This is about building a portfolio.

When do you have a full and finished portfolio? Never! It is always a work in progress, because you are too, always busy improving yourself and working with better people. The trick is to use good pictures to get even better photographers to work with you, and build your way up to a kick ass collection of pictures that represent you, your look, and your interests well.

Check the whole post here.
Check Ancilla's DeviantArt profile and gallery here: http://ancillatilia.deviantart.com/
Last but not least, Ancilla's oficial website at www.ancillatilia.com.
It's well worth the visit!