When you get a new phone or tablet or computer you should charge it to ~80% and then wait until it’s below 20% before charging again. This will protect the battery life. Basically leaving your phone charging overnight slowly breaks your battery because it’s constantly being stuck on maximum capacity straining the internal structure of the battery.
Keeping your devices on WiFi also helps greatly increase the time before the next change
Not quite the same. No reason to discharge it before topping it up. If you do want to top up from 70% to 80&, that’s not a problem for the battery, just perhaps the charging connector if you do that a lot.