The main things are a good work environment (with good lighting!) that is not too cold (don't do it in a cold garage in winter, it can make it very difficult to get the solder to flow properly), a good soldering iron of the appropriate wattage, and good solder ... if you are based in the EU the latter might be your biggest challenge, because I think leaded solder has been banned there. I'm not sure how to use the non-leaded stuff, I think it would create some challenges with regard to temperatures etc. I use 60/40 leaded solder but I am in Australia and I have a big stockpile of it anyway (for the amount of soldering I actually do, which is not often).
Be careful to avoid overheating the pots. Besides damaging the internal components it can also desolder the legs off the pots. That happened to me when I was struggling to solder in the winter when I had to get my guitars sorted out before a recording session. I ended up taking it to my tech and he fixed them.
Sounds like your tech assumed that the colour codes for BKPs are the same as for Di Marzios or Seymour Duncans. They are not.
