1. Make sure you've installed VRCFaceTracking.
2. Make sure you find an avatar that supports face tracking or head movement. You won't be able to check if it works without this/third-party module enabled. Here's a video tutorial: link
3. The most important step is to make sure that you have enabled OSC in the avatar settings and enabled tracking of individual parts of the face/head; by default, this is all turned off.

Follow the order given here and you should be able to install the module and the application.

1. Install FoxyFace application
2. Install FoxyFaceVRCFTInterface module
3. Check Connection
4. Camera Setup
5. Update Babble Model
6. Do Auto Calibration

Instructions can be found here.