Dear Vicky, there was a time when Models had to be beautiful/handsome/fair, etc. Now times have changed and curvy, dark and aged are also walking the ramp. So there is no set criteria to become a model. Yes, one should have a pleasing personality and a good physique because one would endorse products. There are Institutions that offer modelling classes and it depends solely on the city you are living in. The scope for this field is massive and needs connections because for people to know your availability, you should be known and your work should be seen. You should get a portfolio done for yourself and before that you may have to workout.