The best way to start is to just get yourself out there. If there is an audition for plays and or commercials, then go. Show them what you can do. If you get rejected, begin taking acting classes so you can improve.
Be sure you can take rejection. There are many more actors than there are parts, and you may have to audition hundreds of times before you get your first part.
Get photos done for your portfolio and then submit it with your resume to a local agent in your area. Also it would be a good idea to maybe take some acting or music lessons. Find a local teacher, and maybe they can set you up with an agent.