What I have learned is
1) Be prepared to be there for a long time if it's a big swap 2/3 sides, complete reset 4 sides or it's not been serviced in a long time it could be a hour or 2 of work.
2) OPEN THE NEW BOX FIRST. I can't stress this enough don't remove anything until you know you have product to fill that section. (Big bags section reset, small bag section fill in)
3) bring sandwich size bags with zippers tops for old stock and keep receipt for expense (dollar tree is fine) and a basket to throw stuff in as you remove and bag it and bring a stool to elevate the box off the floor so you are not constantly bent over. .
4) I bring masking tape and a marker. I run a piece of tape directly down the middle lightly and write the row numbers on it for a complete reset, that way you can lift it and move it from side to side and you won't have to count everything over and over again.
5) On a regular display tape A,B,C,D on each side so you don't mistakenly place something on the wrong side.
6) Don't feel overwhelmed the first trip is always the longest. I have done both assembling the entire fixture which is 2/3 hours with help and done complete and partial resets, but once your display is set correctly you can usually be in and out in under a half hour on most trips.
Good Luck!