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.