I have heard individuals complain about the battery life of their Apple Watch (or lack thereof) because they feel they need to charge it overnight, but then they don't get their sleep data.
A routine that works well for me is to charge it twice. I charge in the morning as I get ready for the day (shave, shower, etc.) then again at night when I get ready for bed (brush my teeth, wash my face, etc.).
It's always charged and I get my sleep data.
I hope this helps!