What they said is great, I'll only add a little. Though it might not all be relevant to this gig, if you keep going you'll probably run into it.
Don't be the last guy there, ever!
Don't be the second to last either.
Bring your tools and keep what you think you'll use on you.
If you don't know what you're doing, or haven't done it (in a
practical sense) before then ask. No one likes to hear about the guy who didn't suit up his fall prevention correctly or who nearly killed someone by using a bad knot or securing equipment incorrectly.
Bring a water
bottle, if you're on five it's faster than finding a fountain and you won't get lost. I don't care if you hydrate, I care if you're gone for ten minutes while everyone's working.
Get the vibe of the work from how everyone else is acting (I know you're mother said don't jump off the cool cliff, but...). Some jobs are fast paced and you'll get run over if you don't pay attention. Where as others are more relaxed, and some have too many people that you start to run into each other trying to do the same thing. Get the vibe and follow it.
Don't compromise your
safety.
Don't compromise some else's
safety.
Don't be afraid to ask for help (grab me an
instrument, cable, move me six inches, check the
plot,
etc) just be polite about it.
Communicate all movement of large objects (and some small). I don't need to know you're moving a
gel frame 6 inches, but if you count out the stack and take it
FOH, let it be known! I do want to know when there's a rope or cable or pile of stingers coming in, same as a soft good,
batten,
electric, box or rack. If you aren't sure
call it.
If someone calls something, look, process, and acknowledge. But if you aren't paying attention, you'd better not blindly acknowledge it.
Have your name on your tools, or
mark them in some way.
If you aren't going to need it, don't bring it in.
If you're in the air, empty your pockets and secure your tools.
If you're using ladders check them to make sure they are locked, if you're on lifts and platforms know what and where the buttons are, if you're on steel or cats obey
safety features (don't dangle your unsecured body outside of the railings).
Understand the benefits and dangers of fall prevention apparatuses or don't use them, this isn't a time to "work through" something or follow blindly. Of particular debate lately is the integral
safety on lifts and installations of lifelines. If you don't understand what you're doing tell them that you're not doing it, and stick to your beliefs on the subject once you are well informed, someone else can do what you aren't comfortable with.
Make sure you fill out your paper work. If you are doing it on site get there early or stay late, but make sure you have the documents you need.
Don't touch your phone and keep it on silent or vibrate.
Listen.
Be courteous.
Show up sober.
Ask what's next as soon as you finish the
current job, don't stand there unless the person in charge of you is busy (stand in his
vision, or ask if anyone needs a
hand depending on mood of the job and your crew head).
Dress appropriately, if it's nighttime it's going to be colder so wear something warm but not limiting. If it's warm wear something light but covering (personal opinion here, but pants are non-optional in my
book, too easy to get cut up in shorts). If it's raining hard don't drag your wet shoes all over the wooden floor, wipe them on the carpet, and bring a poncho. If it's really cold, bring cold weather work gloves and wear good socks, consider more layers depending on if you know what you'll be doing, like unloading steel from a truck.
Bandanas and handkerchiefs to wipe the sweat off are nicer than using your
hand, but as long as you don't drip on the
plot I don't care.
If you do anything with
gel, ask how they want it done, everyone has a different
system.
Same thing goes for
instrument storage, if it's your first time, ask.
If it's been a while since your last strenuous physical activity, take some time the few days before to at least get somewhat back into it. Sprints around the
block for 15 minutes twice a day, calisthenics while you're watching the news, going for a walk, stretch, or anything really that will elevate your heart rate and help prevent you from burning out 3 hours in during a 4 hour
call.
Don't be rough on the equipment.
If it isn't your department don't touch it.
Pay attention to your surroundings.
Carry a pencil and a
sharpie (notebook optional).
If it involves the
plot or paperwork use a pencil.
If you're grabbing a bunch of things, modifying something at the board, or circuiting hanging at specifics, write it down in your notebook (or your arm) so you don't have to traipse back to
plot/paperwork because you forgot.
Don't smell like a locker room, and don't smell like Ralph Lauren, smelling like a controlled or illegal substance isn't usually good either.
Wear work clothes, and solid closed toe shoes (preferably electrical hazard and
safety toe designated footwear).
Don't wear new work footwear to work, break it in at home so you don't second guess your footing and you don't have that fresh and slippery feel to them.
Women can do anything you can, don't be an ass.
Men can do anything you can, don't be an ass.
Communication with the person next to you is fine, being obnoxiously loud or distracting from your work or others' is not.
If you start doing this to help make a living start bringing a lunch with you don't go out every day.
Being there on time means you are ready to start working, not that you arrived and need 10 minutes to get your gear out, go to the bathroom, and down your coffee.
Pay attention to and respect your elders. There are a lot of old stagehands and a lot of stagehands that have been doing this longer than you've been born. Watch them, pay attention to their methods, ask why on your break, people who love this craft will be willing to help you. They can teach you more about the industry than you think, more importantly a lot of their methods work and they work well.
This topic can go on and on (just like I did), but it can also be summed up pretty simply: be prepared, pay attention, be courteous, be safe.