I never drop a tree without a hard hat on my head. Came by this the hard way when a high branch decided to give it up a try to take me out. Glanced off my head and bounced off my shoulder. I "came to" sitting on the ground with my hand 6" away from the chain on an idling saw. I was sore for weeks. I had the hat but was being stupid. Once the tree is on the ground the hard hat goes back to the saw box
Clear out an escape path before starting to drop
Carry wedges and a hammer with you. Comes in real handy if yer trying to fell in a different direction than the natural lean
Make real sure to not cut the hinge unless yer really sure what that will do. Did that once when I was overconfident and not paying attention and my tree fell 90^ away from the natural lean. Fell on a fence that I then got to fix
Take breaks, stay hydrated, intently study the subject before starting
Keep chain sharp and adjusted
in general, KYHOYA (keep your head outta your a__
More as they occur to me