Install BeatSaberMarkupLanguage using one of the many available mod installers for Beat Saber or download the latest version from BeatMods.
Install the latest release of DynamicOpenVR by following the instructions in the repository's README.
Download the latest release of Custom Avatars and extract the entire contents of the ZIP file into your Beat Saber folder (for Steam, this is usually C:\Program Files (x86)\Steam\steamapps\common\Beat Saber), overwriting any existing files.
To resolve references and automatically copy the compiled DLL into Beat Saber's installation directory, create a file called CustomAvatar.csproj.user next to both CustomAvatar\CustomAvatar.csproj and CustomAvatar-Editor\CustomAvatar-Editor.csproj and paste in the following:
<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<!-- Replace this with the path to your Beat Saber installation -->
<BeatSaberDir>C:\Program Files (x86)\Steam\steamapps\common\Beat Saber</BeatSaberDir>
</PropertyGroup>
</Project>