I should be clear that when I say drive mechanism, the heads are probably the main concern. Extra friction as the tape passes through the mechanism will result in tighter winding of the tape, and you know where that leads.
I also forgot to mention it, but be sure not to leave tapes in the player when you are not playing them, and of course keep out of sunlight (which goes back to avoiding temperature swings). Cool (but not cold) is better than warm.
It was always best to store cassettes on end (upright) so the tape would not slip down from the reels. I would guess the same is true of 8 tracks.
Here are some general care guidelines for magnetic tape:
http://www.clir.org/pubs/reports/pub54/care_and_handling.html
And here is a pretty cool chart of life expectancy for magnetic tape relative to temperature and humidity. I looks like if you keep the humidity below about 35% the tape will last along time (aside from mechanical cartridge issues):
http://www.clir.org/pubs/reports/pub54/estimation_of_LEs.html