Hi Neelam,
This is Himanshu, and I have been in the Training & Development field for the last 6 years.
According to me, to be a trainer, you should be interested in communicating, reading, listening, and observation. If this interests you, then your first step in identifying yourself as trainer material is checked.
In matters of professional training institutes like ISTD, they are of great help; however, they do not guarantee that a great trainer will emerge from 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). The most important thing is that you take up training in which you are interested. For example, I was interested in soft skill training, so I pursued training and exposure in soft skills. I read good articles, practice, books, watch movies, surf websites related to my training material, and equip myself for the same. In that way, you need to strategize your growth and knowledge bank in some way.
My advice to you would be to identify a role model in training and get trained under him/her for the skills/knowledge that you want to impart to people. Don't copy or mimic him/her, but definitely keep an eye on the best and most effective methodologies that he/she uses in the training program. Learn about different trends in training, learn the art of understanding people and engaging with them, become a patient listener, and communicate effectively. Later, if you wish to take up training programs from ISTD, that would be advisable but not at the initial stage.
Have a great time, and I hope I was able to provide an appropriate answer to your query.
Regards,
Himanshu