From TalkBass Wiki
[edit] Shopping list
[edit] Soldering Iron
For the size work we're in for such as building crossovers and repairing cables, a 25 Watt iron is perfect. A generic 18 to 25 Watt iron will also do fine, and are readily available at Radio Shack.
Interceptor bought one of these in 1981. He said it has had a few tips replaced over the years, but it also got daily use for the first twenty years of its life.
[edit] Solder
Two options here; the favorite of us old timers is Kester 60/40, or pick up some generic Radio Shack solder.
[edit] Solder Sucker
Really a helpful thing in the shop, it allows fast removal of solder. I've used a Soldapullet for decades. Radio Shack has some worthwhile devices as well.
[edit] Bench Rest
I use a vintage glass ashtray.
[edit] Third hand
A third hand like this might be helpful too.
[edit] Method
Ok, you've got a brand new iron and the tools, now what?
The first thing is to tin the tip. This is something to get in the habit of doing every time you start soldering, it is the cleaning of the tip and wetting of the iron. Let the iron heat up, it takes a few minutes. While it is heating up, go grab a piece of paper towel and dampen it. Once the iron is nice and hot, melt some solder onto the tip, then wipe the tip clean on the wet paper towel. Clean and shiny tip!
The best way to think about soldering wire to wire connections is to use solder to seal the connection. The connection should have a bit of mechanical "worthiness" without the solder. What that means is as simple as the wires to be joined ought to get twisted together, then soldered.
OK, on to soldering with our nice clean iron. The trick is to heat the work, not the solder. Place the tip of the iron underneath the wires to be joined. Give things a few seconds to heat up. Melt solder by touching the solder to the top of the wires. When you've got it right, the solder will flow readily and when it cools the solder ought to be shiny.
[edit] Inspection Phase
After over thirty years of doing this, I learned that no job is done until it gets through inspection. What to look for here is a shiny solder deposit. Dull means it didn't get hot enough. You can reheat a connection if need be. Sometimes, a little bit of solder melted on the tip is helpful to provide some more hot area.
It takes a little practice, but is a skill that can easily be mastered in less than an hour.
[edit] Solder sucker
Oh yeah, things sometimes need to come apart, that's where this comes in. The basics are to heat the connection and once the solder flashes (gets shiny and liquid) suck up what you can. Some connections will need multiple stabs at this, and you might have to pull on it to loosen things up.
[edit] Notes and references
From Interceptor, from fEarful thread part 5.