Make sure you put your iguana in its habitat or another room and try not to get too mad at it. Assess the situation. If the bite is severe and you're bleeding profusely, you'll need to quickly stop the bleeding by applying pressure to the wound. Assess the situation again. You'll need to decide if the bite is severe enough for a trip to the hospital emergency room.
Iguanas are very capable of delivering that serious of a bite.
Once you get the bleeding to stop, it is now time to clean your wound. You should have all you need in your iguana's first aid kit. This will help your doctor prescribe the right kind of antibiotics. There is much more you should learn about properly treating a bite from an iguana, but hopefully this will help you for now. Melissa Kaplan has a very good article, Dealing With Iguana And Other Reptile Bites that will inform you of a lot more information than we have here.