The first question you have to ask yourself is this:
Can I kill another human being?
If your answer is “no”, you should not posess a firearm.
If your answer is “yes”, then you need to try many, many different firearms....shotguns, pistols, etc to find what you feel comfortable with holding/shooting. Don’t worry about accuracy at first, just feel comfortable.
Then, practice, practice, practice and make it a routine. Practice as least once per month with the firearm. This will force you to clean it and keep it in good order and to keep your shooting skills up.
If your answer is “no”, you should not possess a firearm”
An extremely important consideration. I would add that you might still want to own a firearm for defense against non-human threats; such as dangerous feral/wild animals; assuming that you might not have the same qualms about shooting an animal (waiting for the obligatory post about “Occupy” protesters) as you would about shooting another human.
Ditto to the various training comments which should include a thorough knowledge of any federal, state, local laws that affect the possession, storage, transport or use of a firearm.
Tactical and firearms retention training would also be advisable if you can afford it; and, particularly, if you intend to carry “open” or concealed. (There are several excellent training schools available as well as many books/DVD’s by highly qualified instructors such as Mas Ayoob and the late Bill Jordan amongst others)
Try to find a gun store that has range facilities that will allow you to try a weapon before you buy it; not every weapon is suited to every person. If you decide to buy a weapon, practice and KNOW the weapon well; including how it works; how the safety system works, etc. (In the past week here in VA a man died after he negligently discharged the .40 caliber Glock he was carrying concealed when he attempted to unbuckle the seat belt in his car ...bullet lacerated his femoral artery and his kids had to witness this tragedy as he “bled out.” Note: I like Glocks because they are relatively inexpensive and extremely reliable (and, yes, I know they are REALLY UGLY!). That said, they require some specialized training and the correct type of holster to use/carry safely.