For Armourer role you need to be able to see in the dark. Practice in a basement or cellar, put up some barriers with the light on, ie old weapon parts, porn magazines stacked to the knee, maddie etc and see if you can work your way around.
For recovery Mechanic you must be able to spot a skiff/*******/freckle victim at 1000 yards. Pick on kids at school, leave your bell end a bit ripe for a few days and then try to catch the weediest kid in class, pin him down and introduce him to your gruiere(sp?!)
For technician (especially Avionics/Aircraft) you need both good eyesight, perfect colour and a steady hand. This should ensure you dont paint over the wrong place when you're doing your warhammer models.
For VM, anything will do really, we're not that fussed.
Hope this helps
(for a sensible answer, go to your AFCO - very few of us will remember what we actually had to achieve to get in the Corps. Good luck)