Hi Neelam,
This is Himanshu and am in Training & Development field from last 6 years.
According to me to be a trainer you should see yourself interested in communicating, reading, listening & observation. If this interests you then your first step for identifying yourself as a trainer material is checked.
In matters of professional training institutes like ISTD, they are of great help, however they do not guarantee a great trainer out of them. They provide good learning exposure and environment. But that's not the only way to become a good trainer (frankly speaking I haven't been to any professional training institute). Most important is that you take up training which you are interested to train upon. For e.g. I was interested in soft skill training so I took up training and exposure in soft skills. I read good articles, practices, books, I see movies, surf websites related to my training material and equip my self for the same. So that way you need to strategise your growth and knowledge bank some way.
My advice to you would be identify a role model in training and get trained under him/her for the skill/knowledge that you want to train people for. Don't copy or enact him/her but definately keep an eye on what are the best and effective methodology that he/she uses in the training program. Learn different trends in training, Learn the art of knowing people and getting to talk to them. Learn to be a patient listener. Learn to communicate effectively. Later if you want to take up training programs from ISTD that would be advicable but not at the initial stage.
Have a great time and hope I was able to provide an appropriate answer to your query.
Regards,
Himanshu