Easy answer:
What battery type do you have? If it is one of the newer lithium designs:
Just top it off each time you use it. No real reason not to.
I think it is good to keep it simple, and it is good to know the basics. Personally, I use about 75-80% of my capacity (range) each day, and charge it to 100% ever day. If you are using 50-65% of your batteries capacity each day, you should do the same.
The “discharge fully” rule is for older NiCad designs (i.e. the first set of rechargeable AA batteries you ever bought). I don’t think that applies to you right? So, forget that rule.
Long term storage: ideally keep it around 50% charge, and don’t let it get too low (really, anything between 80% and 35% would be fine). For riding the bike, I wouldn’t worry about running the juice too low, as the system will prevent you from running it too low to do damage. For longevity, you wouldn’t want to run the battery down until it cuts out too often. And, don’t leave it sitting around empty.
To add more detail:
Generally, Lithium batteries deteriorate faster at high levels of charge, or high levels of discharge. So, ideally your battery would spend its life at 50% charge. Any off the shelf battery will keep you from going to low on charge just by riding it (unless you drain it as far as it lets you, and then let it sit around for a year).
If you really, really want to have a battery last a long time, you would charge it up to 85-90% and then not let it get below ~35% power. But, for most people, just charging it up to 100% after each ride is fine.
The better products will let you charge up to 90% (allowing you to extend battery life by not filling it up to 100%), or to 100% (for when you really need it) or to 50% to keep it in the sweet part for long term storage.
(P.S. I use wax in my chains).