It's gotten to the point where it's pretty easy to avoid soldering altogether. IMHO, I wouldn't plague myself by grabbing the torch when doing a repair, and neither do most pros. anymore. I just helped a disabled friend who had an 1/2 copper elbow fail on a supply line in an exposed basement ceiling. I cut the elbow off, leaving as much pipe as possible on one side. I then cut an 18" piece of new tube, and using a Sharkbite 90* fitting and coupling, the job was done in five minutes. Knowing that the work didn't need to be bone dry is a huge plus. I have done repairs with water flowing down my arm while I got soaked. No big deal.
I've also done this work many times, the old fashion way. First you attempt to drain the lines. Then you cut the joint and try to get all the water out. Now it's time to stuff the lines with bread. Now IF everything is sparkly clean, bone dry and the God's are smiling, you will succeed. Unfortunately, the first attempt seems to be a 50/50 shot in my experience.
All I can add to the other soldering tips is this. First, don't do it if you can avoid it, and Sharkbites make it pretty easy to avoid. Second, if you do decide to take a shot at it, use a MAPP gas torch. Much hotter, and WAY more successful. Propane is for cooking hot dogs, it sucks for plumbing work. Good luck.