Honestly, most of it seems to come from kissing ass. I've seen people get tons of green rep simply because they told a certain mod that they're hot, or that Metallica is a really really fucking awesome fucking band, or that Santino is god. This why there's so much sucking up around here. I'm not complaining though, thats just what i've gathered from my time spent here.
People also seem to get green rep by posing more often in the bar room, carrying on conversations with respected posters and mods. You have to be social, otherwise no one will want to rep you.
Also, there are alot of great people on these forums who will rep you for quality posting in the wrestling forums. You have to put alot of work into your posts, and be able to defend your point if you're challenged by someone. If you can't defend your point, no one will take you seriously.
In short, visit the bar room frequently and get to know the mods real well, and constantly tell them how awesome they are. Keep up good posting in the wrestling forums, and you should be able to gain more rep easily.