Warming up is essential before you tackle an intense workout.  It gets your heart rate up and loosens your muscles so you can stretch properly without ripping anything.  The warm up that I am writing in this post will get your heart rate up, loosen you up, and get you ready for your workouts.
Complete two sets of the following exercises below for thirty seconds per exercise:
Running in place
Burpees – for this, add a pushup to it as well as a vertical jump after each repetition.

• Jumping Jacks
• V-ups or In and Outs – If you are already winded, substitute with a standard crunch or sit up routine.
• Footwork Drills – Perform shuffles, hops, bounces, etc., to improve your footwork, but also to get the blood flowing.
• Squat w/ front kicks – Perform a squat and then a front kick.  Alternate kicks after each squat.

After you have completed the exercises above twice, you should feel warmed up and ready to go.  Now you are ready to stretch.