Find a mentor. Choose an English or history teacher -- someone with knowledge of political philosophy and rhetoric. Work with your mentor on setting up a meeting time and a strategy for forming a team.
Build membership. Choose a date for your first debate team meeting. Create a simple flier that lists the meeting time and place and your contact information. State that it's the first meeting and that all are welcome to come. Ask all teachers to pass out the fliers to their students. Get permission from the main office to post the fliers around your school.
Create an agenda for the first meeting. Start the meeting by having your adult mentor explain debate and its different methods. Present a short debate so new members can get a feel for what it's all about. Open the floor for questions and discussion about what kinds of topics students are interested in debating and what they'd like to do in future meetings. Set a permanent weekly meeting time.
Create a list of debate topics. Pair up club members at the next meeting and have each pair debate an issue from the list. Get feedback from your club's mentor on how to improve debate skills. Use an online dictionary and references to check facts and word usage in team members' arguments.
Enter your team in its first competition. Give your new team a couple of months to get comfortable debating internally before competing against another school.