Getting things up and running is a real challenge in modelling.Once things are going well you can gain a real momentum and take off, but getting tto that point needs determination and often a really thick skin.
The most obvious place to start is at the modelling agencies in your home town or on the internet. The best way to start would be to visit local agenices and consider your own internet portfolio. Things can happen on the internet, but a lot of people say that serious models rarely get serious offers just by building up a site on their own and waiting. Of course, you may be in luck and you can get spotted this way, but other approaches are also vital. The modelling agency is of course your best way to get into the industry, but it can often be hard to find an agency that is genuinly good.
To avoid getting scammed make sure you check out web sites which give you info in the kind of scams you may be faced with. That way you'll know a few tricks that you may be faced with later and it'll help you. Above all always be very careful about parting with your money before getting any actual work offers. Remember that a genuine modelling agency receives its income from commission off your earnings. Ask yourself why then do they want money up front - is it maybe because they don't have enough commission rolling through ?
As a final word, always do what you can to update your portfolio. You may be able to find photographers who can help you on a TFP basis - but always go chaperoned. If you prefer, then update your photos at a studio. Also, think about getting a comp card - it's very handy to be able to hand over a card with all of your details on it.
All the Best !