Put your powerbook to sleep. Always. I use this all the time, and it is really really handy.
I have not drained the battery on mine, and they (I have two) are just fine still after 10 months use.
Spinning the drive down...I dunno. I guess you might save some power on that, But if you are working hard on your laptop, you have to wait a bit (a tiny bit) for the drive to spin up. I really hate having to wait for things like these, so I don't spin it down.
You can write discs and recieve mail with the lid down if you have a monitor and keyboard/mouse connected to the book. (use in clamshell mode, or whatever it is called). You cannot have the computer do anything if you have it on its own with the lid down. Lid down=sleep...
I guess you can set energy saver to at least turn off the monitor after a couple of minutes without use and then almost close the lid. Don't know how much heat dissipates throught the top of this 12"powerbook, but if you can use it in closed mode, I guess you should be just fine.
Other tips...hmm.
Get some iKlear (for washing your book). Works really well. Get the spraybottle and cloth, not the wetwipes.
A good bag (willow design has some new nice ones for 12")
Get a tablet! Yes, its great, and I use it all the time both for graphics and surfing...
Don't know what else I can recommend...anything in particular you want to know about???
Ah, yes...spare battery..that's brilliant as well.