See Marilynn Madzar for more info. Think about what students need and want. You could sell snacks or a theme meal. Give massages to stressed out students. Make sure you find a cost effective fundraiser and earn more than you spend.
Communication is key.
Many organization leaders find it easiest to communicate over e-mail which makes it easier to keep and organize messages. Organizations with a focus on socializing work best if meetings are regular. Regular meetings give members a sense of continuity and make it easier to build friendships. Let's say there's a lull in your organization and not much happening. Communicate with your members and ask for suggestions.