Here's a "standard form letter" regarding latex seal trimming:
Be sure to trim your fingernails before trying on the suit. There is sometimes a little sharp corner on the edge of a nail that can act like a razorblade to a tightly stretched wrist seal. Be sure to dust your hands & seals with UNSCENTED talc or baby powder. Most baby powder contains perfumes that can degrade the seals. The "non-allergic" stuff has no perfume. Other lubes, like KY or even aloe vera gel work great.
I use a sharp, high quality scissors but other cutters, like razor blades or Xacto knives will work. Try to have someone hold the seal for you if using a scissors, or stick a can of some sort into the seal if using a blade. Be careful not to over stretch while cutting or the seal might tear.
If you're taking a drysuit course, wait to do the seal trimming with the instructor's assistance.
It's an awful good idea to have someone that has done seal trimming before give you a hand.
Start with trimming your wrist seals; they cost about $15 & are very simple to replace if you mess one up.
A general rule of thumb is to have the neck opening about 2½ inches smaller than your actual neck size. You'll probably need to trim it more though.
Wrists are about an inch & a half smaller for starters. You can also start trimming a quarter inch off at a time, but that can get tedious after the first half-dozen cuts.
Your seals should be comfy enough to wear for 10-12 hours.
Face seal trimming:
Your face opening will sometimes need to be trimmed as well; the bad habit of whacking hoods off was no doubt started by someone not knowing about this. Put your beanie on, pull the hood up & put your mask on.
Have someone draw a line around the mask & across your chin right below your bottom lip. Make SURE there's enough hood material to seal past the beanie.
Fair the lines in to make a nice rounded upside down pear shape & snip away.
The rubber of the neck seals likes to be "warmed up" before donning. You do this by inserting at least 3 fingers through the face opening and into the neck, and giving it several hard rapid stretches before pulling it over the head. Makes for more limber latex, easier to stretch over the head.
