Info taken from an arstechnica article.

Practice shallow discharges.
One of the worst things you can do to a Li-ion battery is to run it out completely all the time. Li-ion batteries don’t suffer from the ‘memory effect’.

Keep your batteries cool.
Even using a battery at room temperature for a year can bring its capacity down by as much as 20 percent. So avoid direct sunlight, cars in summer, …

Use your battery regularly and for small apps.
Running the battery out very quickly by drawing a lot of power at once is another way to cause it a lot of strain.
With a spare battery you don’t use that often, manufacturers say the best way to store it is at 40 or 50 percent charge in a cool place.