The winchester manual pretty much covers the bases (had an FN SLP). Used Tetra gun grease on bolt/bolt carrier contact points. For brass ring by gas port, occassionally brushed the brass ring near the gas port to remove carbon (used Ballistol). Top part of pistons need to be brushed (Ballistol) used q-tips to get carbon out of the piston ports (some recommend occassionally soaking the pistons in solvent on occassion, but never tried it myself). Best to keep lube on the exterior of the mag tube, where the interior of the piston makes contact, to a minimum (I usually apply a very small amount of Tetra and the wipe it off). Cleaned it after each range trip. Have run over 500 shells, no problem.
Brian Payne makes a good point on the pistons.