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Honestly, my only tip is to just put a lot of time into it.
I started 3D with character modeling, which was a lot harder than, say, making basic stuff.  But it made me learn topology in no time. With that came UVs, texturing, and a bunch of other neat tricks.
Before this jam, I hadn't touched Blender in... about a year give or take. So it was basically a race to remember everything I'd learned back then.
If we're talking specifically about the models for games, just goof around for a bit and figure out what suits your game best. Then turn that into a full asset and make the rest of the assets with it in mind.
I spent around 10 hours a day just modeling things for the game and troubleshooting issues with them. And at some point, it drained me a lot.

Thanks a lot.