The other 10% is:
* Mute unnecessary channels
* Turn off mentions entirely for channels where they don't mean much other than "@XYZ is looking at it"
* Set mobile notifications to "only if away" (+ a work hours schedule; if it's important they can click the "notify anyway" link)
* If you're on Android: change the notification sound to something custom that's a lot more "calm" and quieter, because you notice it anyway and it won't give off the "important! DM! check now!" feeling that all of Slack's do. (I miss this on iOS)
* On really bad days (focus-wise): don't be afraid to hide or close Slack entirely to just focus. I usually just put it away in Windows' extended notification tray, so I can occasionally check it without relaunching (or appearing offline/away).