Save to .gitattributes in the root directory of a Unity project. See Using Git for Unity Projects for additional details.

.gitattributes
# Macro for Unity YAML-based asset files.
[attr]unityyaml -text merge=unityyamlmerge diff

# Macro for all binary files that should use Git LFS.
[attr]lfs -text filter=lfs diff=lfs merge=lfs

# Default to auto-normalized line endings.
* text=auto

# Code
*.cs text diff=csharp

# Unity Text Assets
*.meta unityyaml
*.unity unityyaml
*.asset unityyaml
*.prefab unityyaml
*.mat unityyaml
*.anim unityyaml
*.controller unityyaml
*.overrideController unityyaml
*.physicMaterial unityyaml
*.physicsMaterial2D unityyaml
*.playable unityyaml
*.mask unityyaml
*.brush unityyaml
*.flare unityyaml
*.fontsettings unityyaml
*.guiskin unityyaml
*.giparams unityyaml
*.renderTexture unityyaml
*.spriteatlas unityyaml
*.terrainlayer unityyaml
*.mixer unityyaml
*.shadervariants unityyaml
*.preset unityyaml
*.asmdef -text diff

# Unity Binary Assets
*.cubemap lfs
*.unitypackage lfs
# Note: Unity terrain assets must have "-Terrain" suffix.
*-[Tt]errain.asset -unityyaml lfs
# Note: Unity navmesh assets must have "-NavMesh" suffix.
*-[Nn]av[Mm]esh.asset -unityyaml lfs

# Image
*.jpg lfs
*.jpeg lfs
*.png lfs
*.apng lfs
*.atsc lfs
*.gif lfs
*.bmp lfs
*.exr lfs
*.tga lfs
*.tiff lfs
*.tif lfs
*.iff lfs
*.pict lfs
*.dds lfs
*.xcf lfs
*.leo lfs
*.kra lfs
*.kpp lfs
*.clip lfs
*.webm lfs
*.webp lfs
*.svg lfs
*.svgz lfs
*.psd lfs
*.afphoto lfs
*.afdesign lfs

# Audio
*.mp3 lfs
*.ogg lfs
*.wav lfs
*.aiff lfs
*.aif lfs
*.mod lfs
*.it lfs
*.s3m lfs
*.xm lfs

# Video
*.mov lfs
*.avi lfs
*.asf lfs
*.mpg lfs
*.mpeg lfs
*.mp4 lfs
*.flv lfs
*.ogv lfs
*.wmv lfs

# 3D
*.fbx lfs
*.obj lfs
*.max lfs
*.blend lfs
*.blender lfs
*.dae lfs
*.mb lfs
*.ma lfs
*.3ds lfs
*.dfx lfs
*.c4d lfs
*.lwo lfs
*.lwo2 lfs
*.abc lfs
*.3dm lfs
*.bin lfs
*.glb lfs

# Executables
*.exe lfs
*.dll lfs
*.so lfs
*.pdb lfs
*.mdb lfs

# Packaging
*.zip lfs
*.7z lfs
*.gz lfs
*.rar lfs
*.tar lfs

Note: When making changes to .gitattributes, files must be un-staged and re-staged for changes to be applied:

git reset HEAD --
git add -A

Changes can then be verified using:

git lfs status | grep LFS: