To begin soldering you need to have the right tools. There are two primary things that you need for soldering, a soldering iron and solder. See Essential Soldering Tools for additional tools that could be helpful.
It is also important to understand what soldering is. Soldering is joining two metals with a 'glue' that has a low melting point. It requires heat from all metals and especially the joint compound, solder. It is important that all the surfaces reach the appropriate temperatures to allow the solder to bond. If they do not heat up enough the surfaces will not bond appropriately, this is called a cold solder joint.
01 The first thing you need to do is clean both surfaces. Make sure both sides of the joint are clear to the metalic surface (i.e. Strip the wires and brush off the contacts).
02 After you have cleaned the surfaces, position the components in the places where you want them. This is where a soldering clamp or stand comes in handy. Unfortunately, they are not always easy to use when your working inside a guitar with short leads. The best thing to do is arrange everything so you can hold it with one hand.
03 When everything is staying in place, apply a small amount of solder to the tip of the iron to get it pre-conditioned. Apply the soldering iron to the surfaces you are soldering and ensure that the iron is making contact with all of the surfaces. Be careful not to hold the soldering iron on the surfaces too long as it can melt insulators, especially on the small gage wires that are used for guitars.
04 After a few seconds the surfaces should be hot enough to apply and melt the solder. Place solder on the joint and remove the soldering iron. If everything worked correctly, the solder should wick, or be absorbed, into the joint. Let the joint cool for a few seconds, normally blowing softly on the hot solder will cool it sufficiently to hold the joint in place until it cools completely.
05 Next, test the joint. Give the connection a light tug to ensure that a proper bond has been made.
One final point. It is very important to ensure that you have an adequate bond when you are soldering connections for an instrument. If the joint is not fully bonded, you can experience intermittent connectivity and an increase in signal noise.