The others have, of course, got cleaning of the barrel licked in their posts.
I've got a suggestion for you that has worked well for keeping it that way for me.
I shoot a Model 34 in .177, and it achieves a little over 900fps with Crossman HP's. I got great accuracy from it, but after a time it would always deteriorate until I cleaned the barrel again. Looking down the barrel revealed a patch about 3" in from the breech was collecting lead deposits, and this was resulting in inaccuracy once it built up enough. This is a common problem with shooting hard lead (like crossman) pellets over about 900fps.
Reading around, I found a recommendation to use pledge furnature wax on the pellets. Wash em, heat 'em up to dry them, spray pledge while they're warm, and then wait for them to dry. The wax coating won't diesel once it's dried, and it beautifully prevents leadding of teh bore. Should about eliminate the requirement for cleaning.
J