Soldering tips:

1. Choose the appropriate soldering iron. A 25 to 35 watt iron is good for general soldering. Do not use a soldering gun. While you’re at it, get a stand (it will save your tabletop)
2. You should be able to heat a connection to melting temp within 2 seconds (if it takes longer than this, your soldering iron is too small)
3. More damage is done using an undersized iron that is held too long than an oversized iron that is used quickly.
4. Clean contacts, terminals, potentiometers, etc. using a pencil eraser prior to soldering. I don’t recommend sandpaper (as recommended by others) as you can cut through the plating on some components making them harder to solder.
5. 60/40 rosin core solder is fine for general electrical soldering. 63/37 (eutectic solder) is even better as it changes from a liquid directly to a solid with no ‘plastic’ state. (That point where you can’t move anything without the connection looking gray / distorted)
Do not use silver electrical solder. (The addition of silver strengthens the connection, which isn’t necessary for guitar applications and increases the melting temperature) Do not use any solder that is not designed of electrical use.
6. Additional rosin should not be necessary for most connections. Sometimes rosin can help in difficult situations (i.e. tarnished potentiometer backshells)
7. Do not solder by applying solder to the iron. Heat the connection to be soldered with the iron then apply the solder to the heated connection. (The connection must be hot enough to melt the solder on it’s own.)
It does help however, to melt a small amount of solder on the tip of the iron so that the liquid solder ‘couples’ the iron to the connection for better heat transfer.
8. Solder should not ball up on connection. Instead it should flow smoothly around the connection. (additional rosin can help)
A good solder connection should be shiny. If it is dull gray, it should be reheated / redone.


Additional tips:

Take care when stripping back a wire’s insulation. Nicks in the wire strand(s) will weaken the wire.
Apply a small amount of solder to the wire (tinning) before making a connection. This will keep the wire strands from fraying as well as aid the flow of solder when making a connection.
Do not use too much solder when tinning. Solder should not ‘wick’ up under the insulation. (This makes the wire stiff and prone to breakage)

When connecting a wire to a terminal, bend the tinned wire end into a ‘U’ then connect to the terminal. Bending more than 180 degrees will make the wire hard to remove if you need to unsolder the connection. Bending less than 180 degrees will make it hard to hold against the terminal while soldering.

If the tinned wire end is too long, trim before you solder the connection. This will ensure the ‘cut’ end is soldered over and not exposed.

If you use heat shrink, remember to put it on the wire before you solder the connection (Doh!)

Allow a component to completely cool before soldering another terminal on the same component. (i.e. do not solder all three pot connections one after the other)

Do not ‘reuse’ solder from a previous connection. Clean the connection with solder wick or a solder vac and start fresh

And finally, don’t put solder in your mouth, try not to breathe solder fumes, and wash your hands when you are finished. – Lead is bad for you.