This can be dangerous business. That does not mean you must get hurt, but it means you COULD. Always work safely. Taking shortcuts is not expedient, but dangerous.
Consider the typical stage:
The layout constantly changes. On-stage is brilliantly lit but it is poorly lit backstage. In the dark are many hard, pointy objects; there are lighting booms, scenery, cables to trip on, people in black are rushing about in the dark. The orchestra pit might be floor level or 30 feet deep, w/ no railing. Overhead and offstage are literally tons of equipment that may spring into motion without notice. In normal industry, such movements require flashing lights and sirens, but not in theatre.
Consider the work spaces:
The arrangement of spaces changes constantly. Catwalks are 30 to 80 some feet in the air, often with inadequate railings, where we toss 50 lb. weights. Falling sandbags and scenery are stock elements of B movies and Phantom of the Opera; we confront them daily. Our only defense is safe working habits and common sense.
There are many ways to do most jobs on stage, but you should learn how the Local prefers it done; not because it is the "best" way, but because it is the expected way HERE. Surprises cause injuries.
Wear durable work clothes and sturdy boots or shoes for protection. Crushed hands and fingers are the most common stage injury; gloves and care will help.
Try to maintain "situational awareness". That means pay attention to what is going on around you, so you know when to duck! Stay off cell phones, texting devices, and music players unless on an official break. Not only are you being paid for your full attention on the call, but when using such devices you are splitting your attention and CANNOT be fully aware of potential dangers around you. You also become a danger to those working with you. Far too often, the one who pays for a mistake is not the person at fault. Don't hurt someone else because YOU were distracted by a personal electronic device.
When climbing, you must use proper fall arrest equipment any time you are at risk of a free fall of over six feet. Wearing fall arrest is not just smart, its the law. You can't wear fall arrest on a ladder, but DON'T stand on the top two steps (the ones with the safety stickers). And remove any loose items from your pockets when working at heights. Carry ONLY those tools you must have to work and tether them to you somehow, or you risk dropping them on people below you. If you do drop something, yell "Heads" or "Heads UP" as a warning!
If you need to work overhead in an aerial lift, you should get training first on it's safe operation. "Aerial Work Platforms" a.k.a."Genie" lifts must only be used on a level surface and must never be raised without the outriggers in place. Riders of boom lifts ("condor" lifts) are required to wear fall arrest gear secured to the basket.
The trick is using safe working practices at all times, and avoiding unsafe situations. Don't be complacent. If you see an unsafe situation or practice, or are uncomfortable with a task, inform the Job Steward immediately. And if someone is injured, inform the Job Steward immediately about that, too.
Work smart. When lifting, use your legs, not your back. Work together on heavy lifts. If something is too heavy, get help! On ramps, push from the back and sides of large crates so as not to be run over if you trip.
Occasionally we build or repair scenery, and may be exposed to toxic paints, solvents, or chemicals, or welding fumes. In such cases, you need proper protective gear (called PPDs or Personal Protection Devices), ventilation and respirators.
Avoid working while under the influence of drugs or alcohol, including prescribed drugs which could cause drowsiness, lightheadedness, or disorientation. If you DO work under the influence, you WILL be sent home.
If you have problems with any tool or machine, bring it to the attention of the show or venue staff so it may be repaired. Don't just ignore it and don't try to fix it yourself unless directed to do so. And don't mess with gear that is not your responsibility. If there is a rope that is tied off and in your way, don't touch it. Instead get assistance from the department responsible. Same goes for scenery, lighting equipment, etc.
IF YOU DON'T KNOW - ASK! If you feel uncomfortable with any task, in terms of experience or safety or any other reason, the Local WILL back you! Don't let the roadies pressure you into doing something unsafe. There is no such thing as a dumb question, only dumb mistakes and injuries.