Do I let it drain all the way and charge it all the way, or vice versa?
The opposite. Try not to let the phone get to 0%.
If you want to be super crazy you’d charge it from 20% to 80% every day instead of 100% but there’s no easy way to do that so I wouldn’t worry about it. In general just let it get down to 20 or 30 and then charge it. Better than charging it from 80 to 100 over and over.
The phone will tell you it’s at 0% when it’s really not, which will generally protect from any damage you might do, but I’ve read that it still helps to give it a larger margin for error and charge it at say 20%.
One small thing that might help is turn off any quick charging features – or use a low power USB charger that doesn’t support them. You can still quick charge when you are genuinely in a hurry, but if you’re just putting your phone on a charger at night it probably only hurts. This is the only thing I do myself because I’m only charging at night anyway.