Your models must have:
- Only 1 UV channel at [0,1]
- PBR materials only, such as Maya’s StingrayPBS
- No shadeless materials
- No displacement maps, bump maps, subsurface scattering, etc.
- No vertex colours
- No morph animations
- Only one animation track
- No animation loop modes
- No double sided rendering
- Lights and sound are also not supported by GLB/glTF
- Try to limit your texture resolutions to 2048*2048, and as little materials as possible
- Try to limit your animations to no longer than 10 seconds
- Try to limit your poly count to no more than 100k for best performance, and 500k maximum
And of course, make sure your model has proper topology and hierarchies.