Install mods via mod assistant: https://github.com/Assistant/ModAssistant/releases
After installing and doing the initial setup you should install all "Core" mods as well as "Mapping Extension", "Noodle Extensions", "Chroma", and "Song Browser". These allow for some nice effects, extended lane maps, and improved search functionality.

If you have an issue with mods not showing up, first try to run "ipa.exe", which can be found in the root of your beatsaber folder. Typically "...steamapps/common/Beat Saber".
If that doesn't fix it you may need to backup your custom songs folder and do a clean reinstall.

Modding discord: https://discord.gg/beatsabermods

---Where to find songs---

Leaderboards and map ranks: https://scoresaber.com/
Song repository: https://beatsaver.com/

Beast saber is a good place to look for songs and with mod assistant installed song can be added through "one click install": https://bsaber.com/

A nice website useful for finding stuff around your skill level, very good for enlargening pp: https://scoresaber.balibalo.xyz/peepee

A handy tool for getting ranked songs: https://cmlsc.itch.io/beat-saber-song-downloader

You can specify what kind of songs you want to get, ex. top 200 ranked songs. Rerunning the downloader later with the same settings will download only the new songs.

---Controls---

For index controllers the default saber locations are not ideal.
You can use the modified defaults below as a starting point and mod to your taste, just change these settings in the controllers menu:
Position Y: -5.0 cm
Position Z: 3.0 cm
Rotation X: 30 degrees

If you have a Vive you should be using one of the alternative grips styles: https://i.imgur.com/ccFdcVz.jpg
The Vive controllers are much heavier than most and in the default position the center of gravity is far enough away it will make keeping up on faster streams nearly impossible.
While not as necessary there are also a few different styles for rift you may consider: https://i.imgur.com/gB1NSGd.jpg