How do you build up stamina?

[The Wall Is Undefeated!]

Slowly with allsorts of cardio.

Treadmill. Swimming. Cycling. Elliptical. Rowing machine. You name it.
You'll notice that doing a mix of exercises will gradually increase your stamina.

 

[Bledswole]

Cardio
Supersets
Dropsets
Calisthenics killer sets

 

[AquaCityBoy]

stop jerking off