I've had this problem before and here are a few tips ive picked up.

1. Make sure you have a decent soldering torch/gun (I use a 35w for almost everything)
2. Practice! After doing 4 or 5 you get alot better quick.
3. I use vice-grips to hold the deans while im working, helps with the heat and doesnt move around as much.
4. Make sure you have a clean tip! I tin, clean w/ sandpaper, solder and it seems to help regulate the heat better.

hth!