Advice me how to charge to keep battery/phone for years
1. 0 to 100%
2.30 to. 90%
3. 50 to 100%
Is it advisable to leave phone in night with charging
Of those 3 options I would do the second. Try to avoid low and high percentages. I personally usually do 40 to 80 which is easy for me on this large battery.
These days battery don't require constant care. I used a OnePlus 3 for 3 years and the battery is still fine even though I never did anything special. Left it charging overnight, sometimes charged during the day... the only thing I avoided - mainly because I didn't need it - was dash charging (aka quick charging).
You should avoid going too low (eg: less than 20%) and avoid heat (eg: leaving the phone inside a car on a hot day), but that's the rule for most batteries we use on computers, phones, etc.
Asus includes a setting (Settings>Battery>PowerMaster>Battery Care) that slows down the charging speed if you charge overnight. Does it really improve battery life? I don't know. Maybe charging it slowly (which is what this feature does) all the time is better... the "problem" is that this phone's battery is big and it can take over 2 hours to charge it from a low battery state.
Anyway, don't forget to use and enjoy your phone. Phones don't last forever.
It really depends on how you wish to define battery health and for how long you intend to use it -and so on.
The general tip is to not leave your device at 100% for a long time. Even if the charger stops charging at 100%, it will still trickle-charge to keep it at 100% when it is connected.
You may use your Scheduled Charging function to alleviate this - it will reduce the time (over night, or your set periods) where the device is at 100%.