If you are working outside of your shop or garage, running for individual tools can slow down a project. Instead, stack all the tools or toolboxes you will need into a wheelbarrow. Then you can wheel off to the job fully equipped or invest in a rolling project center.
Be sure to frequently check the air filters on your tools. Clogged filters can choke an engine and many filters can be cleaned and reused.
When not in use, keep your work ladders locked up so that burglars cannot use them to break into your house through the upper floors.
Need to replace your trusty old level? You can check it for accuracy. Lay one working edge on a flat surface and check the bubble. Swap it end for end, then check the bubble again. It should be in the same position. Now try the opposite working edge. Take a reading, switch end for end, and take another reading. The bubble should be in the same position. Likewise check for plumb by holding it against a flat vertical surface.
When you want to measure something at home or in the hardware store and you don't have a tape measure handy, try using a dollar bill. It's 6 1/8 inches long and almost exactly 1 1/2 inches when folded in quarters.
If vibration causes nuts to constantly work loose, first add a lock washer, if it doesn't have one. Or, if there is room on the bolt, use two nuts, tightened toward each other so they lock solidly. You can also try wrapping monofilament fishing line under the nut before tightening it on the bolt. Another possibility is to try wrapping the threads first with the teflon tape that is used in plumbing.
Magnetic tipped screwdrivers are handy for keeping a hold on smaller screws, especially in tight places where your hands can't reach. You can magnetize your screwdrivers by rubbing a magnet down the blade five or six times in only one direction. To demagnetize, rub the magnet in the opposite direction.
Keep an extra tool set in your car or truck. Think of it as an insurance policy against road emergencies. You'll be glad they're there when you need them.