It doesn't matter as much if you're not Korean, but a proper manner is always a nice thing to know and abide by.
Assuming that you're drinking some soju with a Korean/Koreans, and they're older than you...
(DISCLAIMER : This is like THE Formal rules to Korean drinking. If you're out with Korean college friends, close friends, etc, it really doesn't matter. I personally don't give a crap about these things unless I'm drinking with someone a lot older.)
Also, try not to get too sloshed.
1. Pour their drinks, with both your hands. Your right hand holds the bottle, and hides the brand sticker on the bottle. Your left hand sort of supports your wrist/bottom of the bottle.
2. After that, they'll pour your drink for you. Left hand holds the shotglass, while right hand lightly hides the brand mark on the glass.
3. Now calling for toast/cheers/whatever to initiate drinking. Even if you don't feel like drinking, at least touch the glass with your lip. It's rude not to drink like that.
4. If you're drinking with someone older/higher rank/etc than you, then when you drink, sort of turn away to the side and lightly cover your glass, as if you're trying to hide the fact that you're drinking.
5. Koreans eat a lot of barfood as they drink. The food is called "An-Joo(안주)". It is very rude to mess with the food. Don't rummage through the pile, just pick a target and snipe.
6. After the first toast, it's not required that you have to fill the glass for the other person. Although I think it's polite to do that once in a while, it's sort of free-for-all drinking after the first shot.
The list goes on and on and on. No, really. There's a LOT more. But those are really the basic rules, and unless you're gonna be hanging out with 70+ year old Korean men all the time, it's pointless.
And last rule : Enjoy the night, but don't drink too much and become a burden.