I think that for one, in order to REALLY get used to how the rules work, you almost need to run a game.
And for another, it all depends on who you game with.
The first game I ever ran came after only playing one campaign. It was disastrous. Girl 1 and Girl 2 had never played. Boy 1 was experienced, but not a lot of experience in 3.0. Boy 2 was also experienced. Boy 3 had never played pen and paper rpgs, but rped online. He and Boy 2 were dating. I never had trouble with the girls. If anything, they didn't get too into the game, because I was too busy focusing on the guys. Boy 1 was fine. One of the best roleplayers I know. But boy two is a gnome-faced weasle. Because he knew the rules better than I did, he could cheat. And he did. And complained every time I made a ruling. And since Boy 3 thought he hung the moon, HE challenged everything I said, despite the fact that he didnt know an AC from a Reflex save. To make matters worse, Boy 2 hated Boy 1 for unknown reasons, so he and his boyfriend ganged up on him. In that instance, it would have helped if I'd known the rules better. I would have commanded more respect from my players, and would have been better able to handle the unruly boys. But in the end, I don't think that the problem was me not knowing the rules, it was my players.
A year later, when I ran my second game, I had a much better grasp of the rules, but I still wasn't entirely up on things. And it went great! My players had low to mid experience, and I had no problems.
A few months after that, with my third game, I had a newbie, a mid experience, a very experienced, and a veteran. The veteran is my DM, and the friend that taught me pretty much everything I know about the game. And that game went fine, too, but was different. The experienced players would point things out that I was doing wrong, or tell me rules that applied to whatever whatever that I missed. But they're supportive, and respectful, and didn't challenge that EYE was the DM, and while I might appreciate a rules reference, I was the one who made the decision.
And in the future, if I run a game for one group I play with now, I'll have to be VERY sharp on the rules, because the group includes powergamers and a dangerous rules lawyer.
So, all in all, I think that as long as you have a group of people who will either learn with you, or, some people that are more familiar with the rules but won't try to take advantage of you, you can run a game that you're not familiar with, and have a pretty good time.