Read the manual completely, more than once. The
PSU and motherboard manuals.
Dont plug anything into the wall until you know
everything is correct-double check.
Before you put the PSU in the case, hold it in your
hands and know what all the connectors are for
and where they go on your motherboard, drives etc.
Double check the PSU voltage switch on the back of the
PSU to make sure its set for your part of the world.
Mine is set for (115V-USA) and not (230V-EU)........
Take your time and dont lick your power supply when
its plugged in.
By the way. Dont buy a used power supply. Save up
and get a new one if you can.
350 watts used to be the norm, but IMO, 500 should
be the new norm for the PSU.