No flux outside the joint. Part of the function of flux, is it draws the solder into the joint. If it's slobbered all over the place, the solder follows it all over the place. (too much flux will also leave you with nasty-smelling water.)
One trick that I learned from an old pro, that helped me a lot, is to look at the color of your flame, where it's bouncing off the pipe.
On the most basic level: if there's any water present, as it heats up the steam makes the flame go bright yellow. Very obvious & noticeable when you know what to look for.
The more subtle thing is that when the copper's just perfectly heated, there's a very light touch of green in the flame - just a tiny bit, where the flame's bouncing off of the pipe... This one took me forever to learn how to spot, and if you've got a whole lot of green, it's too late: the pipe's too hot, and you're boiling away all the flux. Start over (clean, flux, fit, sweat).*
It's well worth it to practice a bit before you try sweating any real pipe. Get a whole bunch of various fittings, some pipe, and set yourself up outside (flux fumes get nasty, after awhile). Try things out, maybe even put some water in one, just so you know what it looks like... get comfortable with it.
I'm beginning to hate copper pipes!
