Don't Fear the Knucklebuster
The adjustable wrench got its nickname from the way its jaws can suddenly break loose from a nut and cause you to slam your hand against the nearest surface. To save yourself from a bruising, position the wrench so you can pull it toward your body. With your knuckles now out of danger, get leverage working for you: Grab the handle as far from the jaws as you can while still keeping a solid grip. If a nut doesn't budge, don't ever slip a length of pipe over the handle as a way to increase leverage. Any fastener that needs that kind of pressure requires a nonadjustable wrench, like a box-end, which is safe to use with a pipe.
Whenever you pick up an adjustable wrench, keep these key three things in mind:
1. Three-point contact
Before you turn the wrench, make sure its jaws are snug against the nut or bolt and touching it on at least three sides.
2. Tighten each time
To make sure that a Crescent-type adjustable has as tight a hold on the nut as possible, retighten the jaws each time you reposition them. Turn the adjusting screw with your thumb while lightly rocking the wrench back and forth on the fastener until it rocks no more.
3. Pull toward you
Whether you're tightening a bolt or loosening it, always try to position the sliding jaw toward you and pull the handle in that same direction. That puts most of the pressure on the fixed jaw, which can't slip.
If clearance for the handle is limited and you can only give the wrench a partial turn, flip the tool over. Wrench jaws are offset 15 degrees from the centerline of the handle; reversing the head allows you to get the most out of each pull. You will end up turning the tool toward the movable jaw half the time, but that's okay as long as you don't have to apply too much pressure.
Keep the wrench's jaws parallel to the work surface. An angled grip cuts down on contact with the nut.