From the MAKE Flickr pool

Mr. Archer tries his hand at this cube soldering exercise – a simple yet effective test of skill.
As detailed in Joseph J. Carr’s How To Design and Build Electronic Instrumentation, 2nd Ed

“There are several reasonable ways to learn the art of soldering, and all of them come down to: DO IT! One method favored by many technical institute instructors is to give the student exactly one foot of 12- or 14-gauge bare bus wire (or insulated wire that has been stripped). This wire is cut up into twelve one-inch lengths, all exactly the same. Why do you suppose that we want exactly twelve pieces, not thirteen or nine? Well, there are twelve edges on a cube, you see. Take these twelve slivers of wire, and construct a cube using solder to hold together the joints. Now, here’s the catch – you may use only a pair of long nose pliers, soldering iron, and solder. No holders, vices, or any other implement! The idea is to teach you not to move the work while it is cooling. When you finish the cube, let it cool (This should take about fifteen minutes if you have been working diligently), and then crush it in the palm of your closed fist. If any of the joints break, get another twelve inches of wire and do it again, and again, and again, until you do it correctly.”

As the first line says, experience is the best teacher here. Tips are helpful, but nothing beats developing your own set of strategies. Lengthy soldering sessions can actually be quite relaxing, even meditative.