Focus on your self-esteem and confidence. Doing well on a leadership skills test is often directly linked to one's self image and ability to show confidence in the midst of a difficult task. This type of work is best done by employing mindfulness throughout the day, "catching" yourself in moments of doubt. A strong leader must be able to trust his or her instincts and abilities at all times; a skill that takes constant practice in order to hone.
Work on your planning skills. Since the primary function of a leader is to quite literally lead a group or individual through a given process, it is imperative that he or she be adept at planning. A good leader will be able to come up with a comprehensive plan, as well as teach the plan to the student in as clear a way as possible. You can practice these skills by completing mock planning exercises.
Discern which parts of the previous leadership skill test you took gave you issues. Many people who take leadership skills tests find that they do well in some areas, and not so well in others. By learning to spot your strengths and weaknesses, you can focus your attention on the areas you had issues with in the past, which will effectively lead to stronger results on your next test.