Both. You need to make sure you can lift at least your body weight and you should run about 3 miles a week so maybe a mile once every few days that way you can increase your stamina so your not out of breath in four downs.
Train your body for the position.
Study your opponent's tendencies.
Think and study like a receiver.
Intimidate the quarterback.
Know when to intercept and break up a ball.
You should do drills like running backwards and turning around while doing so. Also you should Play basketball and focus on rebounding this will prepare you for grabbing the ball out of the air with others trying to get to it befor you can.
