When you say "GPU settings" what are we talking about?
If you mean in game settings (things like shadow quality, that sort of thing) then as @Frag Maniac
says it will depend on the game.
You could try using the "high" preset in most games (maybe "medium in some modern AAA titles), and then adjust settings up or down depending on how it performs.
There are also articles on line that discuss performance in specific games. PC Gamer, Techpowerup, and DSO Gaming are some of my go-to sites for that. e.g.
Need help navigating RE3's unintuitive graphics menu? Here's our advice.
Beyond Blue is a single-player narrative adventure game that takes players deep into our planet’s beating blue heart. The game is currently available on Steam, and E-Line Media has provided us with a review code. As such, it’s time to benchmark this game and see how it performs on the PC...
If you mean settings for the graphics card itself e.g. settings in the graphics card software, then generally you might leave them to default unless there is a specific issue you need to deal with.