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.
Perhaps the biggest issue regarding firearms ownership for self-defense is most certainly NOT hardware selection, but MINDSET!
The best book I know that discusses this issue in a clarifying way is Masaad Ayoob's In the Gravest Extreme: The Role of the Firearm in Personal Protection
While the book is getting a little dated on things like the aforementioned hardware selection (revolvers were still really big, pistols not so much), the sections on mindset and legal consequences are still very much worth the price of admission. I would say this writer should buy a copy of this book now.
“Can I kill another human being?
If your answer is “no”, you should not posess a firearm.”
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“Do not buy a gun for protection unless you are prepared to make the instantaneous moral decision that a human being threatening your life with a weapon has now lost his right to life.”
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Corollary: A woman found dead in an alley, raped and strangled with her panty hose, is somehow superior to a woman explaining how she scared off her attacker with a gun she wasn’t willing to use to shoot him.