I start with concealable test. If it is too big or heavy I avoid it. I am not going to conceal a 50 AE Desert Eagle, or a Model 29 Smith in the Texas summers, and we do not have much of a winter here.
I look to make sure good holsters are available for it.
I make sure it is south paw friendly. (I am a lefty shooter.)
Make sure it fits my hand well enough to shoot with.
Then I take it to the range.
It should eat any ammo I feed it like a greedy pig in a trough of slop.
It should line up point of impact to point of aim out to 25 yards with the ammo I will carry in it.
If it fires 200 rounds of my practice reloads (hand loads with the bullet profile, and velocity of the carry ammo I am going to use in it.) I will carry it.
I shoot at least 1 magazine a week to keep familiar with it, and to assure that it functions as it should.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.