I found that people will just follow the nearest person moving roughly in the same direction as you want, if you can't see no one doing that, you then muddle your way through people but then find that theres a train of people behind you.
if you cant't find anyone to folow and you're the front person, then simple rules seem to come into action eg angles of how people are stood also seem to play a part, you prefer to go around the back of people rather than in front of them. and if there's two people together you try not to go through them. etc..
this knowledge is based in the UK where people are somtimes too polite