I always walk it, usually two or three times. The first time, I get the sequence into my head. I try to remember each individual fence by some characteristic. For example "White gate, then bend around to red oxer, roll back to triple combination".
It makes the jumps more individual, than just looking at an arena full of jumps. Pick out something identifying for each fence. Usually colors, or the type of jump. If it is a gate, a flower box, an oxer, etc.
Then the second time I walk, I get down the angles I want to take, how close I want to cut the corners, and make sure my approaches from these angles/corners are straight.
Then after doing this I might stand outside the arena and go over it a couple more times in my head. The distances, angles, corners, and the sequence of fences. :)