LOL. Where to start. LOL.
If you are trapping creeks, Get yourself a pair of safety Glasses. When you are bending over and stick a piece of Brush in your eye, and scratch your Cornea, you will appreciate this tip. LOL.
Practice your set makeing year around. And if you have the capabilities, Video tape it once in awhile. you would be suprised at how much you can learn by watching yourself make a set. sometimes you think you are doing one thing, but you are really not, or you are doing something else. the video will allow you to see these things and correct them before your season starts.
Never ASSUME that anything you dispatched has expired. ALWAYS check to make sure with a stick or your gun barrel before you get too deep into the catch circle.
Study Missed catches. Don't just go stomping into the set when the trap is fired and nothing there. LOOK in the dirt and mud around the area. Learn to read the set and understand what happened. Did the animal Dig the trap, if so how did it react before it dug it. Did you get a flat out refusal, if so how did the animal react. Maybe you have over guided, or maybe the lure was too strong, or what ever, but look at the tracks and try to determine what happened. There is NO BETTER TEACHER THAN THE ANIMAL ITSELF!!!
Many times, Less is more with Lures.

This is not my tip, but it was on the traps 4 Kids video's and it is a very good Solid tip. When trapping beaver, Try not to do it alone, and if you are, or even if you arent, Take a length of rope and tie it to a tree on the bank, and around your waist, so if you fall in you have a way out. Unfortunately, when you fall in to the cold water, you don't always have as much time as you think to recover from the shock of the cold.
NEVER reach through a hole in the ice to check your 220 or 330 when it is attatched to a pole, or staked on a drowner. If you stick your hand into that trap thinking that it was already set off and it wasn't, you are in some big trouble if you get caught in that trap.
If your state has requirements for distances from Beaver Dens and Dams, Carry a tape measure, and DON'T test the distance. If it is 15 feet, don't put the trap in at 14'6" and think that the DEC will let it slide, THEY WON'T!!.
NEVER turn your nose up to someone who is giving you information or advice about makeing sets. It may not all be good information, but it generally isn't all bad information either. When you think you know all there is to know about trapping, Sell your traps, and get out of it, cause your and idiot. LOL>

I bet there isn't one real trapper on here who will not tell you that they learn at least 1 thing new every season.