Leadership activities should generally have defined goals, decided upon by the youth or their leader. Sometimes a goal will be more quantifiable, such as "Organize basket bingo to raise $1,000 for the Boys and Girls Club," and sometimes the goal will have to do with a lesson, such as "Learn how to write donation letters, approach local businesses, find space for auction, advertise, determine roles, assess costs, find volunteers, pack and decorate baskets on time." An activity may have one goal or many, depending on the type of activity, focus of the leader and other constraints.
Once your group and guidelines are established, try to guide the youths more than you direct. If on a ropes course, do not tell the youths how to get the whole group over a barrier, but ask questions to help them find the solution to their problem. Because meetings can easily turn into hours-long affairs, you may need to direct more in this area. Teach the youths how to run a meeting and let them do so most of the time, but make sure you intervene and guide the conversation back around to the topic at hand when exchanges get heated or speakers get off topic or long winded.
The best lessons often come from experiencing something, not hearing about it. The same applies to making mistakes. Your youths will have a deeper understanding of the problem and a better learning experience if you allow them to make some mistakes on their own. Do not, however, allow youth to do something that will cause injury to themselves or someone else or create another hazard of some sort. Also, remember to temper guiding with allowing mistakes, and do not "guide away" all problems.
Make sure that your youth leadership activities include post-activity reflection. Either talk with the youths or have them talk amongst themselves and present their conclusions to you. If their activity was something that they did, such as a challenge course or learning a new skill, their discussion should center around how they felt during the activity, whether there were any conflicts, what they learned from the activity, and how all of it applies to leadership. If their activity dealt with planning something, their discussion should cover what went well, what did not, and what they would do differently and the same way should they plan a similar event in the future. Reflection is an important part of leadership because it helps fine tune planning, can help people put themselves "in another person's shoes," teaches to think critically, and helps streamline thinking.