A small caution - While you can get "electrical" solder at the local lumber yard, the stuff that comes in big spools is usually intended for soldering house wiring and such. It is likely to be a 70/30 or worse, and may have a "core" of pretty low-grade "resin" flux.

For soldering "electronic" stuff - like cables, you want to be sure that you get a true 60/40 solder with "electronic" grade flux core - or solid wire with some good brush-on flux that you can apply separately.

Be sure you do your soldering in a reasonably well ventilated area, especially if you're using normal 60/40 tin-lead solder. The fumes should be minor, but there is always some lead (and flux) smoke.

There are also "lead free" solders on the market now, but I haven't tried them.

Especially on stuff like shielded cables, there are times when solder is the way to do it, but if you look around you can probably find crimp-on connectors for almost any kind of connection you need. They're the "modern way," and if properly crimped are generally much more durable and reliable than a soldered joint.

A common "error" when working with shielded cable is "cutting the shield" down to a few wires. If you strip the insulation off the outside of the braided shield, and push it back so that the braid "opens" a little, you can use any "small pointy tool" to open a hole through the side of the braid - about a half-inch back from the end, and pull the center wire(s) through the hole. Then when you pull on the (now empty) braid, it collapses down to a "wire" that you can "tin" and solder, without loosing pieces of wire from the braid (and without having a lot of "little pointies" sticking out of the solder.)

As Guest Q said, the critical thing is to get the wire clean enough (and use an appropriate flux) so that the solder "wets" the wire when it melts, get the solder melted fully, and I would add, once you remove the heat - don't move anything until its fully cooled. Clamps help sometimes.

With some cable, it's almost impossible to get the wire hot enough to solder without "melting" the insulation for a ways back from the joint. A clothespin (spring type) on the insulation near the joint can help keep it from overheating - if you encounter that problem.

If you're splicing in the middle of a cable, be sure that you tape it enough (or put a short "shrink-tube" on) so that the cable is a little "stiffer" around the joint than the rest of the cable. It'll last a lot longer if the solder joint isn't flexed.

John