When soldering the wires "tin" them first by putting the iron under the bare end and run a bit of solder onto it, then do the same with the back of the pot or lug or whatever, then a dab of solder on the tip of the iron and put it face down on the pot beside the spot you just "tinned" once the tinning melts dip the tinned end of the wire into the solder pool and once the solder flows together remove the iron.

There are heaps of tutes on YT, do a search for Dan Erlewine who has some excellent stuff there. Also you could search YT for " high performance soldering " at one stage I had about 3 hours of it on NTSC video tape in my tech training room for the new starters to get them up to speed