For me it's pretty specific because I go to college in a city and everyone lives close to eachother, but...
You go to one party, you chill with people there, you continue on going to parties and ****, you just lay down some "game" or whatever you want to call it on girls at these different events, and then at some point leave together. Usually the "leaving together" thing happens after the party has moved to a club/bar. Also, of course, you can get the number at any point along the way (usually I leave that 'til I've been at a gathering featuring this girl twice or three times) and progress from there.
Others will have more interesting techniques I'm sure, but I basically go to all parties, all potlucks, all nights out and you start seeing familiar overlaps of people between the different friend groups. So you don't even bother with the phone number or the date or any of the bull****. Loose connections, lots of loose connections all the time.
Also note that this is perfect because it's just an extension of my social life. AND note that you have insta-social proof because you hang out with so many people that you have respect with all kinds of groups. Sweet.
And again, note that unfortunately my "model" of doing things isn't applicable to all college people.