Use an Impact Driver When You Can
An impact driver and a set of high-end hex-shaft nut drivers are all you need to loosen small nuts and bolts. For larger nuts and bolts, you'll need an impact gun and a set of six-point, impact-rated (black finish) sockets. Ordinary chrome sockets can't handle impact work and may crack or shatter under the stress. And because impact-rated sockets have six points instead of 12, they're less likely to round over bolt and nut heads.
Stuck Fasteners Can Bite You
When it comes to causing pain, stuck fasteners can get the job done. Right when you're giving a stuck bolt all your muscle, wrenches will slip, bolt heads will snap off and your hands will get smashed against something sharp. So always wear gloves and try to orient tool handles so your hands will be clear if a tool slips.
Needless to say, pounding on stubborn fasteners with hammers, mallets and sledgehammers poses similar dangers. Never use a regular hammer for metal-on-metal impact. Bits of the hardened metal can break off and become embedded in your flesh. Safety glasses are a must, as well as hearing protection when you're running some of these very power noisy tools.