Accelerators with PAL chips will most likely to croak and hard drives that run 24-7 are most likely to take a step closer to their grave. Otherwise, like I did with my other amigas, watch their voltages, keep it clean from dust and dirt, check their fans and your Amiga will last longer than you think.
Unfortunately, I may have to throw out one accelerator card for my 2000 unless I find a way to keep those PAL chips from failing when they start to heat up. I had the cover off and placed fans over them while I had it running, but if I need to keep the cover closed, it won't help at all. I'll try to use retangular chip heatsink fins and see what happens.
The very first sign that your old hard drive starts to give you trouble, back all your valuable information and get a new one.
Replace batteries that leak immediately and clean the board with 1. Isopropyl alcohol and 2. rinse with 50/50 alcohol/water. Make a label with a date to replace the battery 5 years from today and place it on the case of your Amiga. If necessary make a quick-disconnect plug for the battery and the board.
Replace any bad fan immediately with a brand new one. Make sure you match the same volume air flow as it says on the label.
:-)