Just to add my two cents worth.....

When I started soldering, I was running into the same problems - cold solder joints, no solder joints, etc. All the tips above are pretty good. I won't debate any of them.

I just wanted to add that I use a silver solder called Stay-Brite that I got from my LHS, It comes with solder and liquid flux. I only need to use a 140-Watt soldering gun and get very good solder joints. I haven't had one break yet.

As everyone here has pointed out, cleanliness is the key here. Mechanically clean the pieces with steel wool, sandpaper, etc., and then use the flux.

I hope this helps somewhat.

Bob