It's all about experience, but really, it's not a hard job even for someone who hasn't done it before.
As i said, you remove the strings, take off the pickguard, you look at the original pickup, see where the wires go, and it's a straight swap. Hold the tip of the iron on the solder joint until it releases the wire, then solder a little solder onto the new wire, hold it in place, heat it up until it "melts" into place, then leave it to set for 5 seconds, repeat with other wire.
It's that simple.
If you know the dangers of using the tool and avoid them, then it's always a simple task, whatever you do.
To fail at soldering, you could push the hot iron on your paintwork, push it on your hand, or push it onto anything that would burn, but aslong as you don't do those, you'll be fine.
