It's one of those don't ask us, we'll ask you. Knowledge is one requirement, personality is another. If you are someone who is constantly yelling and swearing at people you don't agree with, we aren't going to ask. In general if you provide help, are polite, and seem to have a good knowledge then you might get it. We aren't always looking for mods however.
"Funny" story about my asking, I was somehow marked down as someone who was asked and said no. No clue how that happened, but it stopped me from becoming a mod. I don't know for how long but I suspect years.