What you will need for soldering guitar PUPS.
25 watt soldering iron (Smaller ones are a hassle)
A clean bench to work at.
An old towel to rest your guitar on to prevent marks (If it's a rear mounted cavity that is)
A pair of tweezers to hold the wires (Or you WILL burn your fingers(
Solder braid (Instead of a suction gun)
Wire strippers
Insulating tape
a pair of sissors (To cut the tin foil on Dimarzios) and a small pair of snips for excess lenghts.
Solder wire with flux is less hassle than seperate no clean flux and no clean solder
If you don't clean the pots of old solder (Depending on the amount) you WILL have to keep the iron on longer to melt the old solder damaging your PUP wire insulator in the process. also the possibility of dry joints etc will occur
TIP
If your soldering a scratchplate type RG get a connector for the
jack socket so that you can easily disconnect/reconnect the wires (saves a bit of hassle).