I'd say with any plated version make sure there is no finish on the threads. Fastech somewhat rrecently stopped shipping the versions with the clear coating and I'd be willign to bet its because it stopped it from firing.
Just about anything acidic will clean oxidation off copper, Ketchup is a great example because it has alot of vinegar. Believe it or not, if I am out of isypropyl I'll use vinegar to clean connections.
When assembling, You want to attach the correct tube for your battery. The "core" tube (the one with the engraving) should obviously be on the bottom, then attach the approriate tube (the longer one for 18650, the shorter one for 18500, NONE for 18350). The Beauty ring (the shortest) is optional and not required. If kicking, add the shortest ring to either the 18350 or 18650 sizes, or use the longer tube for 18500.
Then, set that aside and take oyur top cap. Completely unscrew the contact pin (but do not remove it) and begin threading your atty until it seats to the cap. Then, screw the center pin in until you get a good contact. I like to turn it a little more after that, that way its less likely to move.
attach the top cap to the tube assembly, then insert your battery through the bottom of the mod. Positive side up. IF oyu have a kick, inser the kick via the top before attachign the cap, then insert the battery.
The bottom switch will need adjustment. first, try screwing on the switch through the bottom until it seats on the battery. If you cannot actuate the switch and make the mod fire, you may need to unscrew the center pin a bit. If you seat and the switch doesnt go in enough (you got quite a bit of overhang or long throw), youm ay need ot screw the center pin in some. If the center pin is screwed in all the way and the switch throw is still a bit too long, consider attaching the beauty ring.
After that, it should be assembled ^^
Forgive my spelling errors, I'll throw up pics after work if peoples want.