As I recall you are in your teens, so you should be able to increase your stamina rather easily. What type of Cardio you do will depend on what you like, If you like to ride a bicycle then you can do that to increase your cardio, jog, walk, climb,skate,rollerblade,row, use a climber / stepper, whatever. other sports, like soccer, football, basket ball, anything that gets yu moving and increases your heart rate will help. what about practicing at home throwing kicks and punching a targetbag, or for 1minute as fast as you can throw and kick, at a heavybag thta wears you out . what do you think?