The oldest way to go about it is to visit them. Book an appointment ahead of time by phone. Bring at least 2 pictures. They don't have to be professional pictures. A head shot, natural and clear. Also a full length shot that somewhat reveals your figure, a clingy dress , swimsuit, figure flattering clothes or other tight fittings garments should be worn. Forget about baggy clothes! It will tip off viewers that you have something to hide. Ask lots of questions. Ask to see what work their models are currently doing? Ask for names and phone number of clients and call them to verify the information, be concerned if they promise you work right away or promise you high salaries. If they don't allow you time to think about it or if they use pressure techniques to sign the contract, be concerned. They should not ask for money up-front for classes or training. Be concerned if the they claim to be looking for ordinary people. Reputed agencies/coordinators might have open interviews during the week, give them a call and find out. Also you can send your photo and resume as mentioned earlier.