I'm no battery expert and don't pretend to be. All devices I have ever had going back to my Palm TX are put on a charger while I sleep each night whether they need it or not. I have never worried about whether I should let them drain more before charging or about leaving them on the charger when they are full (because I'm asleep). And sometimes I top off during the day if it's easy. I have always gotten good mileage out of my batteries doing this (My Nexus One was going strong at the end of 3 years, my Nexus 7 2012 at two years is also doing great). I don't take lots of stats about my battery life and am really not very analytical about it at all.
I have no idea if what I do is recommended, but it works great for me and requires very little keeping track of things or thinking on my part.
YMMV