1. Wear eye protection:
a) Every time you use a power tool.
b) Every time you use a hammer.
c) Every time you're using a tap or other brittle, hardened tool. They can, and do, shatter.
d) Every time you're under a vehicle. Falling dirt and debris can go anywhere.
e) Any time you're in the shop and you think that there might be some small chance that something could break, spin off, or fall and end up in your face.
2. Ear protection is a good idea as well. Ever used an air chisel or air hammer?
3. Filling the void in a set of diagonal cutters with silicone will keep small bits of wire or zip ties from being flung across your truck or garage. Split the silicone with a razor once it sets.
4. Grinding the face of a pair of diagonal cutters flush will allow you to remove welded-on studs and trim wire ties without any tag ends.
5. Paint or mark with colored tape the stops on your jack stands with different colors or with numbers so that you can easily level your truck once you jack it up.
6. Add about two feet of pipe insulation to the bottom of your jack handle. It will prevent the handle from denting the rockers or roll pan and it costs less then $2.
7. To start a nut at an awkward angle, put a loop of tape, sticky side out, in the socket. It will stay in place until you get it threaded.
8. If you've got even less room to work with, use a ratcheting wrench and use tape to secure the nut. It will come unstuck once it gets threaded on.
9. When you're taking something apart, take photos of the process. Digital cameras are cheap, and digital photos are free, so when it comes time to put your truck back together you'll know what it looked like when you started so you don't end up with "extra parts".
10. Along the same lines, bag all of your fasteners in zip-closed sandwich bags and label them with a permanent marker. If you've got the photos and all the fasteners, you'll have a much easier time re-assembling your truck, even if it's several months later.
11. Before using a hole saw to cut a large-diameter hole, cut a small hole near the outer edge for the metal chips to fall through, it will speed up the cutting.
12. Drilling two extra holes close to the pilot hole will also allow you to grip the piece and remove it from the hole saw once your cut is finished.