It's the same as for 2D jams: make sure you know your tools, and that you can make a good estimate how long a task will take.
Especially for 3D art, there are some tasks that may take longer than the entire jam if you go in depth (like sculpting, retopologizing and texturing a detailed character, rigging and animating non humanoid characters, etc), so cut corners there. You can use low poly style objects, or non animated objects (like vehicles and robots).
Regarding programming, there's not that much difference between 2D and 3D in terms of workload. Just make sure you know the how to work with the engine's 3D tools, and with 3D transforms.
(I'm assuming you work in an engine like Unity or Godot here - if you're creating your own engine it's a different story!)
Background: I prefer making 2D games, but two of my games here on itch.io are 3D games that were made during two day jams, with a group of two or three people (one artist), using Unity. All art assets were made during the jam, and we hardly used any starting code, though one game was extended a bit afterwards. Check them out on my profile if you're interested.
You can also look at the results of past jams here on itch.io, and see what's feasible in a short time period, though you never know how much was premade.