What i normally do is hold the wire gently with pliars, and then silver the tip of the wire's exposed part. If you don't know what that is, its when you put the wire tip on something you're not afraid of damaging, (wood surface, old desk, etc.) and apply solder to it.
After you've silvered the tip, heat up the casing a bit, and apply the now silvered tip of the wire to the case. Then hold the soldering pencle on it until it melts. as soon as it melts to the case, take the pencle away from it, and gently hold the wire to the pot using the pliars until the solder dries (1-5 seconds).
I do all this with an 80 wat radio shack soldering kit, and it seems to work out quite well.