The most useful thing to have on set is the one thing you can't get in film school, which is experience. A veteran willing to share their wisdom is as valuable as a year's tuition, in my book.
Since this is, of course, just a blog, I can only offer the next best thing: a great article written by Dr. Fred Ginsberg, C.A.S., PhD., entitled Introduction To Pre-Production Planning for Audio. He covers set etiquette, hierarchies, and generally stuff that can bite you in the behind if you happen to be fresh out of school and new to the pro world.
There are no apologies nor excuses run under the dailies. Good sound is always expected (and taken for granted). Bad sound, on the other hand, is always attributed as your fault. You will never heard [sic] it said that "even though the soundtrack was poor, the Mixer did a good job considering that we made him use bad equipment and no boomman." Instead, they will remark that they should have hired so-and-so, since that Mixer did a fine job on the last shoot.
Pay attention, kids. This is the kind of stuff that can save your future career from being a non-starter.
Link to article, via equipmentemporium.com. Many useful articles in them thar hills, so be sure to dig around the rest of the site as well.