No, not a plea for help - a resolution!
I've always struggled with this - I've rewired lots of guitars, and while connecting wires to lugs has never been an issue, I've always struggled getting solder onto the back of a volume pot to earth.
I now know what I've been doing wrong - it was the solder.
With my latest Charvel rebuild, I decided to order some solder along with all the other bits from Axes R Us. The solder they supplied has a rosin core, and it worked perfectly - did exactly what it was supposed to do, made a nice covering on the back of the pot, allowed for really easy connections.
If you're struggling, I'd strongly suggest testing a few different types of solder.