I was in student organizations for years and I can tell you biggest mistake that people make is that you never ever measure your success as an organization by how many people show up to your meetings. There's no value in having someone gawk at you, your officers, or a guest speaker for an hour a week.
There's only one thing that matters in student organizations: Output that will help you in your career. Once you graduate, how large your mailing list is is a trivial matter. You goal is to churn out as many resume bullets and connections that you will be able to use when you get a job.
Secondly, people who just show up to your meeting to stare are going to waste. Give them something to do. Also, you should have means to allow people to propose their own ideas.
Thirdly, accountability is everything. Learn parliamentary procedure and take minutes. In the organizations I was involved with, and project/event we started had a charter that specified who was in charge, who was working on it, and a specific outline of the scope and timeline. Projects always go to hell and the first thing people do when things go wrong is not make things better, but start pointing fingers. Make sure people who are honest and responsible are protected.