There is no single major thing that you can do once to help you out, but there are two major practices that you can do to improve battery life:
1. Do not leave you iPod constantly plugged in or docked, and do not charge it every night. It is perfectly fine to leave it off and use it for a few days without it being charged, it will help your iPod, not hurt.
2. Calibrate your battery about once a month. To calibrate your battery, use the iPod until you are told to charge it (battery level 0%), then plug it in to your computer and let it charge completely before removing it, and try not to use it while it is charging.
And as a combination between both points, I would not charge your iPod until the battery turns red (less than 20% capacity), that way the iPod gets nearly a full cycle between each charge. With the battery life of a classic, you should be fine for a day of just music or a short video or two using it while that battery is red, and then just charge it that night, a battery at 20% or less will last you for most of the day if it is just basic usage.