[gRoberts84]

I set my notifications to "Direct messages, mentioned & keywords".

This way, you can keep it open and dip into whatever you need to but you'll not be swamped with millions of notifications.

I'd also go through all channels etc and mute or leave channels you're not actually required in any more.

[throwaway91021]

I have it set to "Nothing" but whenever I have the window open, I can see the orange notification conter popping up on several channels (even if I mute them).

I tried leaving channels but I get invited back whenever people tag my team, so I gave up and muted all of them (but still get the notification counter, which makes muting useless for me).

EDIT: Whenever someone tags my team, the little Slack icon on the tray bar goes red... and I don't know if that's a direct message (usually important) or someone tagging my team just "fyi". I have to check it always.