Most of the candidates choose the best NDA coaching center in Delhi and also many coaching academy are available in Delhi. Such educational academy’s training is useless because they only provide general coaching. Which is not the best criteria at that time, what king of coaching and training are required for NDA examination.
Well the written examination is only a part of the NDA selections and I would term it to be relatively easy, with or without coaching. I would not say that the coaching centres are worthless as your environment plays a large role in contributing to your results and some teachers and fellow motivated batch mates can really help you push through. You can study yourself too and its not going to be tough but you might take a little longer to reach similar results.
But getting to the main point which is the physical selection round. You really need to tone down your body fat to get those pull ups in. Mind you, many rural kids apply for the NDA selections, and all they have been eating is dal(lentils) and rice their entire life and well, they can run pretty damn fast. Of course the average guy living in Delhi would be lacklustre in comparison. Apart from that in the 100 or so selections many seats are taken away by candidates having contacts and whose relatives are in the military. So you really need to perform well in the physical to get selected. The written exam is just a (rather very meagre) part of it.