* big caps that can contain high voltages even when a device is powered off, in TVs or microwaves.
* Know where a fire extinguisher etc is, keep them near the workbench.
* Keep the workbench clean, tidy and well-vented.
* Don't panic when mistakes are made. Slow down instead of doing a quick-fix.
* I like a big red button to power down everything instantly. Can be just a switch on a plug box.
* an isolation transformer - meaning you must now touch both conductors to get shocked instead of just the live one
* a foot switch to control the power supply - serves as a "dead man's switch" to cut power in case of an accident
(these are not mutually-exclusive, you can combine them)
Risks to consider in general are (also of the top of my head don't take as exhaustive):
* Electrocution
* Burning yourself
* Setting stuff on fire
* Fumes, both from soldering and overheating/burning plastic
There's a kind of balance between habits and awareness. Rely too much on awareness and you will miss some safety issue during a complicated repair. You need good habits, but rely too much on them and you won't notice when you finally make a mistake.
Those apply during repair processes. It's also possible to render a device unsafe to use, for example by damaging a li-ion battery or by a 'bodge' repair that circumvents a safety feature.
Reminds me of the comments I read on a video of somebody doing something unsafe - "safety squint".