Accept all gambits except the Queen's Gambit.
And even that is not a "true gambit" lol - plus Accepting the Queen's Gambit is still playable as long as you don't try to hold onto the pawn forever. The lines that score well in the QGA tend to give back the "extra" pawn to catch up in piece development, but I think both declining it and accepting this c4 pawn is fine if you aren't greedy either way.
Also a bit more of an "advanced thread" based on the level of debate, but I created this thread a long time ago and asked what gambits are solid or not. My fundamental orientation was that all gambits were dubious. However, a lot of experimenting, studying and strictly defining what constitutes as a "gambit", I have come to the conclusion that some gambits are objectively sound. I still believe that most are not however; the few variations I consider solid are not even typically what one thinks of with a "gambit."
https://www.chess.com/forum/view/chess-openings/sound-gambits-2