Tin your leads. Melt a bit of solder onto the bare wire ends, that is.
The backs of pots can be tricky. Scuffing the area you want to solder to with some sandpaper and getting a blob melted on there before attaching your pretinned wires is well known trick.
Heat the component, not the solder and do it as quickly as possible.
Don't breathe heavily on anything and turn the ceiling fan off to avoid cold solder joints. The solder needs to cool at it's own pace. Cold solder joints are dull instead of shiny and are not mechanically or electrically sound.
Invest in some alligator clips or some other appropriate small metal clip to hold things together for you as you solder.
30 watt "pen" iron for pots, caps, jacks, etc. Larger wattage guns can be used for speakers as they are fast, but never near pickups as the field those windings give off can demagnetize pickups or so I've been told. Not that you'd want to use such an overpowered awkward tool for inside the control cavity.