People run for office for a number of reasons; make sure that you're doing it for the right one. Make no mistake, campaigning is tough. Opponents might spread rumors about you, and with all of the hard work involved, you grades could suffer. If you have a strong motivation, though, such an issue you care about or a strong desire to "be involved," this will help you get through the more difficult times.
Your school likely has set up strict rules governing what you can and can't do during your campaign. Make sure you understand these rules clearly, and make sure your friends and others helping on your campaign do, too.
You can't win an election without a solid plan. First figure out who is likely to support you. Usually these are people who are most like you. For instance, if you play a sport, you might target members of the athletic teams. Second, figure out a message that will win over these potential supporters. For example, ask yourself if one issue among those you care about is one that they care about as well.
Campaigners and marketers talk about message delivery in terms of multiple "touches" in multiple "layers." This means that you should "touch" your potential supporters with your message many times before election day, and that these touches should be delivered through various media. Your campaign plan should include which posters will go up where, when your Facebook group will launch and how you'll invite people, and other message delivery issues.
All your plans and message delivery won't matter if your supporters don't vote on election day. Make GOTV, which stands for "get out the vote," a priority. Try to get all of your supporters and friends to help you deliver a special GOTV message on election day in many layers (something like "Today is election day! Don't forget to vote for me!"). Meet supporters at their lockers, put up new posters and perform other attention-grabbing activities. Every vote counts -- work hard for each one.