First be sure you are wearing headphones. Next, if you're getting a lot of bottle caps in a certain range, try using Iron Audio for a quick check. I forget from time to time and still dig one, and there are a few that are alloyed with aluminum or something else that can fool me, but I'd rather dig trash than miss jewelry.
Besides, there is a lot of trash that sounds and ID's like a good target; an example would be what appeared to be an aluminum screw-top that sounded a little off, and it turned out to be a nice large man's gold wedding band. That made for a nice day!
With experience you can minimize digging junk, but unless some incredible new breakthrough technology comes along digging trash is just part of metal detecting. I listen and look for consistency; digging trash is just part of the game, and actually, I'm glad, as if the good stuff truly stood out, anyone could come along and easily cherry-pick it up. In that respect trash is actually your friend. If you want the good stuff you have to dig the junk!