Before importing your avatar to Unity, make sure the head and body are merged and use the name 'Body'. This is important for the armature, but also if you want to use Face Tracking
Click on the fbx file of the avatar in Unity and make sure "Legacy Blend Shape Normals" is checked under the 'Model' tab.
Making a quest version? For transparents, make sure to use the following shader:
"VRChat>Mobile>Particles>Multiply"
How to add face tracking to your avatars: