Like in a toetouch, and in any jump, you should stretch really well. A good stretch to do is a hurdler stretch. With one leg bent in back of you, stick your other leg out straight in front of you grabbing you ankle, toe, or calf. Hold for about 20 seconds.

When attempting a jump, you must have a prep. The two preps can be found  here. After you have chosen a prep that is comfortable to you, attemt your jump.

In a herkie, one leg (which ever is more comfortable) should be extended to the side of your body, while the other leg is bent to the side. Don't forget to point your feet.