NEVER run the battery to empty. That is the fastest way to destroy a Li-Ion battery.
If you are not going to wear your Apple Watch for sleep monitoring, then put it on the charger every night so you are in the habit.
If you are going to wear it for sleep monitoring, the make sure you are using an 18watt or higher power supply, so you get fast charging, then charge it while getting ready for bed, then charge it again while you are getting ready for your day.
Or find some other daily charging habit, as over time, your Apple Watch will need to be charged daily, and it is best to establish your habits now.