Before you choose a martial art to study, get into shape first.
Start lifting weights and build up your cardio.
Build up your hand strength so you can knock people out. The stronger your grip, the harder your punches will be.
Buy some hand grips to help with that or do the old school boxing exercise of hitting a tire with a sledgehammer or just do weightlifting with no gloves on, that'll work ( you'll have calluses on your hands but it'll work) go for it!
Also build up your neck strength so you won't get knocked out in a fight. You can do this by purchasing a neck strengthener. I buy most of my boxing equipment off the title boxing website.

YOU ARE READING
Jason Buff's self defense guide to Kicking Ass
Non-FictionJason Buff will show you how to properly defend yourself and look good doing it