I know this may sound silly, and you already know, but use your resources! Utilize your vendors, facility personnel, past committee members, and even students to create a great event.
One of the most frustrating pieces, especially as a vendor, is seeing planning committees come in and try to recreate the wheel. It makes complete sense to come in and try to improve upon previous years and Beat the Jones’ per-se, and create an event that is better than the previous year. This is not necessarily the best course of action to take. Some processes and procedures are well in place, and should not be changed. For instance, the planning process. Still allocate the one person to talk with vendors and take the committee’s ideas back to them. Know the spaces you’re utilizing and what worked well and what didn’t from previous years, and, most importantly, what the student’s enjoyed the most/least.

Themes certainly need to change from year to year, but if something wasn’t well received, figure out why. Was it the placement of that item/activity? Was it not working properly? Was there staff/volunteers to explain the methods?
Once you’ve troubleshot the different elements that were ‘not a hit’, expand on those and make this year better!
Always stick with a theme, and if you have different rooms for different themes, make sure to utilize those resources again. If you’re doing a carnival don’t throw in something that doesn’t fit just because it ‘sounds fun’. Staying within the theme will allow a more cohesive event, and won’t confuse guests and cause you to re-evaluate next year to know why no one liked the Racing Toilets because it was a Casino Royale themed event.
Use your vendors to your advantage, ask what they’ve seen work well in the past as well as their feedback on certain items. If something sounds great, and fits with the theme, but is best for a different age group, maybe need to consider the different options that you are offering guests. Overall, just make sure you’re not starting from scratch, especially when it comes to the facility of use, committee members and those guests that you are trying to keep engaged and around for your After Prom.