If you have the time (40 hours) a NREMT First Responders course is well worth the time. If not, there are courses by the American Red Cross and American Heart Association that take just an evening or two and will get you through the basics. There are numerous others out there as well of varying quality. Try to find one through a local college or university, emergency medical service (ambulance or fire department), or hospital. Make sure you find one by an instructor with proper credentials as there are a lot of fly by night courses offering questionable information.
You can also get first aid and first responder books online that meet the DOT and National Registry of Emergency Medical Technicians (NREMT) guidelines. Mosby, Brady, and AAOS are well respected publishers of emergency medical texts. Be careful about books written by individuals who are not backed by a recognized emergency medical organization. Same goes for websites. Unfortunately there is a lot of outdated and just plain wrong information out there.