Couple of things with spring-piston rifles:
1. NO dry-firing! That piston slams up against the
end of it's run with no air cushion, and eventually
things break. If you try it once (or by mistake!

),
you'll be able to feel it right away.
2. NO petroleum-based lubes in the chamber. Dieseling -
sometimes damaging is the result. There's a synthetic
chamber lube available - look at the sirgun sites. Its'
not needed very often. If the piston seal starts to squeak on
cocking you'll need some, but it'll take a lot of shots to
get to that stage.
3. Probably not the best idea to store it with the spring
compressed. It may or may not hurt it, but I always store
the gun with the spring in it's relaxed state.
4. Position and hold: Do what you should be doing in the first
place! Forward elbow directly under the piece, forward hand is
"dead" (not gripping the forearm in any way, just acting as a
rest), pull the stock into the shoulder, but not quite as firmly
as with a conventional rifle, and a good cheek weld. Follow-through
is MUCH more important. That pellet is only moving 600 or 700 fps
(or maybe 1000 in the more hi-powered guns!), so it's in the barrel
longer. Anything you do while it's in there will affect your shot
placement - probably negatively.
-Stretch