Avoid flash if you can. My prejudice is that it's better to use fast film and push it. Not only will you be less obtrusive at the event, but the pictures will look less snapshotty. If you do use flash, be sure the people in the picture are all about the same distance from the flash so they will be lighted equally. If you must bring some people together for a group picture, have them put their drinks down, or at least lower them.
Nothing looks tackier than a row of people staring at a camera with wine glasses in their hands.
Not much can be done with a handshake, but try to catch it an instant before the hands clasp. Try some unusual angle, perhaps one that shows the audience and thereby gives a sense of the total event. Have them walk toward each other and meet at a designated spot. Before putting too much energy into a shot of one of the deadlies, though, rethink the need for such a shot at all. Group Shots Group pictures are particularly challenging.