-Look up a video, how the game actually runs before you decide to buy. I mean, some people tend to over-estimate Steam Deck capabilities, when they write about them, but video just shows the real capabilities for each game.
-ProtonDB is your best buddy. You can find there settings, that will probably suit Deck the best. Expecially nice for begineers, who don’t have the “know-how” with performance and quality impact of each setting.
-Don’t be afraid of desktop mode. If you intend to use Deck just as a gaming device, you’ll be satisfied. But it can do more. A lot more. Maybe you could even grasp some Linux basic skills just by playing with your Deck’s desktop mode. I personally do computational chemistry and oh boah, how Deck could be useful even for productivity tasks.
-My list of Deck recommended games (look them up in Autumn sale): Red Dead Redemption 2 (runs exceptionally well and looks gorgeous on Deck), Cyberpunk 2077 (used to run poorly, but with 2.00 update and SteamOS 3.5, it runs and looks great), Witcher 3, Wolfenstein: The New Colossus, Mafia II, L. A. Noire, Tropico 6, GTA V…
Cyberpunk 2077 after 2.00 update and RDR2.