Start with your feet a little wider than shoulder width apart, while maintaining posture bend your knees and assume the squat position. Swing your arms back, tighten your core, and then jump explosively while swinging your arms forward to gain momentum. As you are landing, assume back into the squat position and this is considered one rep. 8-10 reps is a set and 3 sets is enough to become sore. Some tips while doing squat jumps are to make sure your knees do not go out in front of your toes. When this happens you tend to put too much pressure on your toes causing you not to gain the full potential of the work out. Also be sure to keep your back straight throughout the whole exercise, as this can cause back pain.