For starters, never, ever go to a rock/pop show without hearing protection. If it's a club situation, never sit near the speakers.
Be rigorous about length of exposure to louder noises. If you do listen to several things loudly, stop after that and give your ears breaks.
Don't mix or jam all day without frequent breaks; you'll just keep turning up the volume as your ears get tired.
If you use headphones a lot, clean the pads and innards on a regular basis with something like Windex.
Bacteria build up in there and get in your ears; repeated ear infections can kill your hearing too
(Which brings us to: keep your ears clean, and get tested on a regular basis.)
If something you own and listen to distorts (not the intentional kind) get rid of it. Distortion plus volume=
highs gone in your ears.
Don't use in-ear 'buds' with Ipods or the like in noisy environments. You are firstly overriding the ambient noise, so you are already loud, and then you add the 'comfortable listening level' and you are way above what you should be.
For the Harley riders: yes, an excellent way to go deaf.
Your bikes hurt my ears half a block away; no amount of money would get me (and my ears) on one of those.
Finally, be very aware of ringing in your ears, like when you lie in bed at night and it is quiet. A little ringing is a warning that Tinnitus could be on the way.
Basic stuff, but it never hurts to repeat it.
Best,
C.