Tips for writing about leadership skills

Be unique.

don't be afraid to brag some, but don't be boastful. also, don't undervalue something you've done (i.e: if you helped organize a run or something of the nature, took pictures for it, did publicity, etc, don't just say that you volunteered some time helping with a race)

Talk about responsibility. 

How it might not have seemed like a big deal to others (working at a pizza place for example) but it was important because you were an important part in the community.  You got to know your co-workers and manager well and learned something from them.  You got to know the frequent customers.  You went above and beyond.  You had to balance work with school and were successful because you planned ahead.  You improved operations or solved a problem and were commended for it.

Or for community service talk about how it was something you were very passionate about and your enthusiasm was infectious.  Talk about how other people weren't giving much effort at first but you motivated them to put together this project and it was a huge success.  You enjyoed taking a leadership role, working with others, and were very happy with the outcome and were commended for it. You can talk abotu how something went wrong and you fixed it only if it wasn't your fault that it went wrong in the first place and you definitely took the appropriate action.

You don't want to come off as bragging or self-aggrandizing.  You want to show that your someone who takes pride in what they do, your enthusiastic, your very responsible, your appreciative of your opportunities and the help you received from others, and that you can reflect on the situation and realize what made it successful and perhaps what you would improve on in the future.