Find a reason to train. Take up a social sport and you will have more motivation to train as you will see the benefits when you play.
Boxing is a great start. Learn the basics and then start practicing by yourself on bags wherever you can find them. Pretend your doing strikes to people you hate and the time flies! ..... whats that ? your a labor voter *BAM* *BAM* ..... Oh I'm sorry Alanah are you building another trainline *BAM* *BAM* *KNEE* *BAM*