My 50/1.4 has seen regular use since I bought it in 2003 or 2004. And it was used when I bought it. Still working great. It doesn't get any special care. Here's some easy as pie tips that might help to keep yours alive and working:
1. Always use the matching lens hood. When shooting, it nicely protects the front of the lens from bumps. When reversed for storage it nicely covers and protects the manual focus ring, which seems to be one of the lens' weaknesses, where the USM gets damaged if the ring gets bumped while the lens is in a camera bag, etc. To me this isn't any sort of special care. I use their respective hoods with all my lenses most of the time... and store them with their hoods reversed. So, for me it's just business as usual to do the same with this lens.
2. Before storing the lens, always set it to infinity to fully retract the front barrel inside the outer barrel. Bumps on the inner barrel reportedly are another weak spot. This is another thing that's nothing special... I pretty much do this with all my lenses, since retracting them makes them as small as possible for storage.
3. Try to avoid manually overriding autofocus with this lens. Even though it's a USM, which means it should allow what Canon calls Full Time Manual (FTM) override of AF, this lens uses a hybrid form of USM and folks who have overridden it a lot say it's prone to more rapid wear and failure. Once again, it's not something I've personally found to be a problem, since today's AF is faster and more accurate than I ever was shooting manual focus lenses. I might occasionally defocus a lens and use AF to refocus, just checking accuracy. But apparently I don't do this enough to damage this lens.
Note: Canon micro motor lenses are not FTM and must never be manually overridden without first turning off AF at the switch... Failing to do this and treating them like a USM lens will cause AF damage and failure. According to Canon, STM lenses are not FTM. However, some people use them that way and haven't reported failures. Because STM are "fly by wire" lenses, the only time you can override AF is when the AF is active... or by flipping the switch to manual. It's not like the USM lenses, where you can simply turn the manual focus ring any time and the lens will respond. As I understand it, the STM lenses need to either be "powered" or switched to the MF setting, for the focus ring to be at all functional.