If it's
brand new, fully charge and discharge it. NiMH should be fully cycled once every three months or so, NiCad once a month. Beyond that, charge/discharge can be pretty much random, so long as you're not severely overcharging or discharging way too fast. Of course, you've got to make sure you have a NiMH charger... trickle charging is definitely not advised because you won't be able to tell by heat when it's fully charged, and the possible overcharging will damage the battery.
If you feel like reading,
http://www.batteryuniversity.com/