As jewelers, we often learn how to solder tiny things very well, but may struggle to apply that knowledge to soldering larger pieces. When soldering large bezels or boxes, use two torches to evenly heat the metal - one torch underneath the piece and the other torch heating from the top. Be sure to keep your flames moving, so as not to overheat one area of your piece; the idea is to heat the whole area evenly, encouraging the solder to flow.
When soldering large joints, cut your wire solder into 1/4" lengths and place them every inch or inch and a quarter. The solder will flow and run more smoothly than if you were using tiny solder pieces every half inch. One 1/4" piece of wire solder will run an and entire inch! No need to over-solder and clean those joints up later!