I feel like everybody who labels themselves a "nice guy" are using the label to hide a lack of confidence and self respect. I used to do that, and to an extent still do ( and probably always will), but I've been valuing things sort of differently as of late and it really helps me make decisions to do what I want to do, even if it's rationalization of awful actions (which is a lot of the time, honestly).
The way I've been looking at is that I'm going to have to initiate 95% of the time, because if I didn't I obviously didn't want to do it enough. There was a girl who really liked me and tried to initiate numerous times, and I blew her off because I didn't really like her. The opportunity to have a real relationship was right there, completely tangible, yet completely undesirable on my part. If I wasn't interested enough in her to actually try to start something, the relationship wouldn't have gotten far because I wouldn't have cared enough to keep it up or would find myself regretting being with someone I didn't like.
The other thing I've been thinking of: Rejection doesn't mean anything, because there's no tangible loss. It's not as if the person you were talking to will never talk to you again, and, if you were "friend zoned", you're hopefully still friends. It might be uncomfortable the next time you talk, but it'll eventually be pushed to the back of their mind or you can bring it up and make the point that you don't want it to ruin your friendship. If you really liked each other before, you will now, even if the other knows you, at one point, harbored some romantic affection for them.
It's sort of like this: You're at a roulette table and the wheel's going, and you're offered a free bet. There's an ever fluctuating chance of winning, but you don't lose anything if you act. Indecision will only make you feel like you didn't lose, and is purely a comfort to people who were to afraid to try. This isn't to say you shouldn't mull it over and look what's still on the table to bet on, and by all means do so to increase your chances of winning, but you have to take the chance to win.
(Disclaimer: I'm in highschool and have very little, if any life experience. I've also been operating under the pretense I'll never see more than a few of these people again, and I can do anything I want socially other than completely vilify myself. I am at a table with a blind dealer, to extend my roulette metaphor.)
EDIT: This didn't make it in there but seriously, LordBucket usually gives out good advice, if only to try if you're in any sort of schooling situation where in all likelyhood the people you're surrounded by won't pop up again or matter in the long run. It's really fun to see how it works out if you have an interest in "active group psychology" (doing things to see what other people will do in that situation).