Find a well-run range. Take a safety course. Learn how to shoot various firearms by renting them at the range and have a qualified instructor help you. Pick ones that fit your physical capabilities. You'll soon enough know which weapon with which you are most comfortable (say that 3 times real fast). As others have stated, simple - safe DA pistol or shotgun with small shot - but use what feels best to you. And practice. Don't forget to purchase plenty of rounds and come back to the range now and then to brush up. And before you buy, brush up on your local and state firearm laws (the range instructur should be a big help there as well).

It's a large mental and social committment when you purchase a gun, so consider all variables that you can *before* you buy. Be prepared for WHAT *could* happen, including defending your life by taking another, or the accidental harm that could happen. Always - Always verify your target. I like the light idea mentioned earlier. As a long time gun enthusiast, whenever anyone tells me that they are buying a gun for the first time, my first question is not a breathless "which one!" but a subdued and thoughful "why?"