Practice, practice, and more practice! 
You’re never going to get good at anything if you don’t practice! You’re going to be tired but nothing is ever easy in cheerleading. You can work on your leg muscles by doing squats and leg lifts and click here to search for more.  Make sure you stretch your hip flexors and hamstrings A LOT! Also, if you jump with ankle weights on for awhile, and then take them off, your jumps will go a little higher (: Make sure your form is good!