I've answered this before, but I think I'll answer it again and make it public for future browsers.
Once, I'd take whatever I could get in a friend, being desperately lonely and hugely needy. One learns a lot of hard lessons that way, so I do have a fairly rigorous set of standards now that I'm less of a walking disaster area.
To be my friend, you must BE my friend...you must reciprocate the relationship, not, of course, on a point-by-point system, but, generally, if I'm putting in a lot more than I'm getting back over a long period of time, even if the neglect is entirely benign, I'm going to walk away, for my own mental health. Even now, I still have trouble with doubting whether even my best friends would REALLY be there for me if I had to call them at 3am. I hope they would be, but I wonder sometimes. Reciprocity is REALLY important to me.
You must be fundamentally kind, compassionate, of good will. (Note: there are people who may consider themselves this that I may disagree with. My opinion is going to matter most when it comes to my choosing friends, of course!) This will make up for a number of other problems.
Ideally, you will be accepting of the wide diversity of human experience...you will understand that what works for you may not work for someone else and vice versa and that's okay. You will try to refrain from concluding that things are "wrong" because they make you uncomfortable or don't fit with your worldview or religious beliefs.
You may not want something to continue going on in the world, and certainly not practice it yourself, but I expect a genuine effort to understand where other people are coming from and give them the benefit of the doubt as much as possible.
If the thing harms only the person engaging in it, leave it alone. If it harms others, then feel free to campaign against that, to that extent. If we have huge disagreements on what constitutes harm, we'll probably have a problem.
Don't be deliberately ignorant and don't be horrendously materialistic or selfish/self-centered.
Don't be self-righteous or overly self-congratulatory (with the corollary that too much humility is a bad thing, too.)
Beyond that, there have been exceptions to every generality that have thrived.
In the end, all we can do is try each other out and see if it sticks, which I am pretty much always willing to do. :)