Be sensible. Tell people how it is. Tell them, "Look, I can't promise you new soda machines or anything like that, because that's an unreasonable and impossible thing to promise. I can promise you that I'll work hard to create fundraisers so that we can make money for our class." Remember to repeat your name a couple of times throughout the speech so that it sticks with people. Let your fellow students know that the money your class makes is going toward THEIR prom, so it'd be in their best interests to elect a candidate who's actually going to do the work. Have a plan and let people know you have one. Assure them that you have ideas and goals that are attainable and reasonable.
Basically, if you let people know that if they vote for a crap candidate their prom is going to be in the gym, they'll be a bit keener on voting for somebody serious.
Practice your speech. Don't become flustered or read the whole thing off of notecards. Make sure you know what you want to say and that you say it loudly, clearly, and confidently. Nobody is going to vote for someone who blushes and stutters and fumbles with notecards and papers throughout their entire speech. Look into the crowd (or camera, based on your school's budget, lol) and don't fidget or squirm. If you want people to see you as a leader, you have to look like one.
I know it's nerve-wrecking to give a speech, but I'll tell you a trick that works every time for me. Pretend you're someone else. Pick a confident, intelligent character and give the speech like you think they would. As strange as it sounds, Hannibal Lector and Dumbledore are my favorite two to pick. They are both extremely intelligent, charismatic (even if one of them DOES eat people, lol), and they make you want to listen to what they have to say. This may sound like a strange method of giving a speech, but it really works. Try it when you're practicing your speech in front of family/friends. You'll be pleasantly surprised.
