My method is to use categories (which btw, you can backup, they're in the steam/userdata/lotsofnumbers/7 folder so just back that up in case of Steam shenanigans) to manage my Steam library. I do it like this:
*Cleared
*Re-buys (games I played already on another platform, but may want to play again on PC)
*Junk (I'll NEVER play these, some I've tried and some not)
*Want to play (this is the big one. I look at every one of those games and think "I really want to play this)
*Maybe want to play (this is for all those bundle tag-alongs, purchases you slightly regret, etc.).
Then whenever I want to play a game, I start in the "want to play" category. I probably won't touch "maybe want to play" until I have no "want to play" games. That way my backlog seems much smaller, and I actually want to play all the games in it! Mediocrity can wait (likely forever)