Always have a real good plan before you start moving stuff around. That goes for cutting and bending metal or moving a motor, all the way down to running wire.
If your gonna chop up something, sit on a bucket, stare at it till your head hurts, and think about how it's all gonna go back together. Do it again tomorrow. (A beer helps sometimes)
If you deviate from the plan, it's probably gonna cost ya. A small change in one place can mean a major pain somewhere else - that goes for about anything.
Glass doesn't bend.
Keep your head out of the rotational plane of anything that spins fast. And your body if possible. Especially wire wheels - your wife will be po'd when little wires show up stuck in all the laundry.
Grinder sparks will eventually catch stuff on fire, even your frayed jeans. (and melt the cell phone in your pocket)
Anything that spins can catch loose clothing. Sometimes even tighter clothing like a T-shirt that can rap up and start to choke you.
If you have air-ride, make sure everything is out from under the car before you lower it. Especially air hoses and electrical cords. Did I say air hoses?
If you plan to chop something, make sure you'll fit in it comfortably and you can see out the
windows.
Welding sunburn on the tops of your feet hurt worse than the ones on your arms.
A frame swap probably is harder than working with the one you have.
Give yourself a couple extra inches space for the motor.
Don't pull out all the drawers of your tool cabinet at the same time.
Roll your project outside as soon as you can so you can step way back and get a good look at it.
S10 frames are ugly.
32 Ford grille shells don't look right on everything.
Parallelogram steering linkage makes it impossible to have good proportions on a fenderless rat. (had to look up the real name - typical A arm steering linkage)
If you don't weld that well, hire someone that does for the critical stuff.
A transmission hump in a channeled cab takes up a lot of foot room.
Stitch welding - find another simple task to do so you don't rush it. I usually sort bolts, clean, etc. in between welding.
Try to spend most of your time standing in the middle of your shop trying to remember where you just put that last tool you had. Or maybe keep your shop cleaned up.
Post lots of pics on RRR.
Have a build thread and ask lots of questions.
The longer you don't work on it, the harder it is to get back to it, or the easier it is to ignore it.