Is it someone I've been friends with since college?

I don't have a regular group, but I'm quite open, anyone is welcome at my table. I have the advantage that I tend to play one-shot or short games, and if I happen to have a player at the table I'm not completely ok with, it doesn't have to last long.
There's also to distinguish between people who are unpleasant and those who aren't good at playing. The latter I generally manage to handle and help, the former... to be honest, I can't remember playing with shomeone who's unpleasant as a person, I guess I'm lucky ^^

Depends on the group. For my main group, it seems to be people we've known since our university days. But we're getting a bit small, so I'm considering proposing we invite two people from my church, though that might be a very different dynamic.

But other groups have other criteria.

I haven't had an organized group in a few years, just a few short games with a few old friends, thanks to life problems. I generally feel people out carefully when I do put together groups, usually having a get together or two before actually putting together a group (playing board or card games to see how competitive, cooperative etc they can be).

We tend towards a low tolerance for absences when I get a game going, so scheduling is vital. Also since we generally host in our home we expect good behavior, no smoking, no drugs or alcohol at game (or coming to game in an inebriated state). We avoid rough physicality, shouting, cutthroat competitiveness with the other players, murder hobos or folks that can't be bothered with remembering their materials or who won't make an effort to stay in contact between sessions etc.

We also remind folks that our game is not a dating service (this was an issue occasionally when I used to accept more college students in my games).

I admit I should get better at one shots. However, I try my best to do enough of a sandbox that it could be easy to join up/leave on downtimes.

So I really hew towards OSRIC. If I talk with people who do game and think they would be good for inviting (all the usual personality/comfort boxes are checked - you know you all have 'em wink), and they have played some other games I give them one of these (sometimes both):

https://lithyscaphe.blogspot.com/p/principia-apocrypha.html - which has a ton Ton TON of links in it to other good principals.

or

https://www.lulu.com/shop/matthew-finch/quick-primer-for-old-school-gaming/ebook/product-3159558.html

Whoops! Forgot to say at the end of the above; if they seem interested in those pamphlets and like what they have to say then that covers it for me.

However, I need to get my brain around more games...so those would find me being a player looking for a GM that would have to submit me to their criteria!

I use one-shots as a way to see how the chemistry between the players is/will be. If someone clearly doesn't fit with the rest of the group, I don't invite them to a non-one-shot-game.

It's a lot harder to do on the board game end of things. I try to maintain an open table policy, and it's rarely bitten me, but once in a while, you get That Guy ...

@Eric Franklin that is DEFINITELY the reason for the criteria.

I guess maybe I am more a bit of a monkeysphere style person. If the friend is trusted by me (actually a friend) and they bring along a friend, that is generally okay.

I can't trust that friends will get along with other friends - I have at least three distinct circles of friends (and I try to make sure each RPG group I run contains members of at least two of those circles).

When I say, "Distinct," I mean, "Don't know and/or have never met one another." Sometimes a mixture like that can be volatile.

I've had mostly good luck so far, but the exceptions to that have been ... notable.

I run a lot of public play events. Over time I get to know the regulars. Many I enjoy gaming with. Over time if I find I get along with someone and enjoy playing games with them then I may invite them to my house for a game night or two. That usually starts with big party like events with lots of people. From that subset there will be people I invite to smaller events.