From Carter Shore

1) Use the smallest iron you can find. My favorite is
an Antex 15W (yes, 15 watts) with a 0.075" tip. You
seldom require a larger iron on circuit boards, only
for large or unusual components, or mounting hardware.
When your iron is not being used, turn it off. The
tips are consumable, and melted solder left on the tip
will dissolve the coating, or turn into dross. The
small irons warm up in a minute or so, so there's no
excuse. 

2) Get small guage rosin flux core solder. I use 18
guage Kester. Larger solder has more thermal mass, and
so it takes more heat to melt at at the joint.

3) Keep a moist pad to clean the tip of the iron. A
small sponge is good, but a damp (not wet) paper
towel, folded to around 3" x 3" works very well.
Inspect the tip often, and remove any dull/extra
solder and debris by wiping lightly with the pad. The
tip should be shiny before you start to solder each
joint. Tin the tip as needed (apply a fresh layer of
solder to the tip by just touching it with the end of
your solder)

4) Let the iron do the work. Touch the tip to the pad
and/or component, maximizing the contact area if
possible. After about 1-2 seconds, when you see the
color of the plating on the pad change, touch the end
of the solder to the joint. As soon as the solder
melts and starts to flow out, add just enough extra to
wet the joint fully, without 'blobs'. The best joints
will show a slightly concave fillet between the
component and the pad. 

5) *DO NOT* hold the iron to the pad for more than a
few seconds. The bond between the copper and plastic
of the board will fail, and the pads and/or traces
will lift. You can tell from the distinctive smell
when this happens. If the solder fails to melt and
flow into the joint, then something is wrong that you
must correct. Adding too much heat will definitely
damage your circuit board.

6) Use a lighted magnifier if you can. You have to be
able to see what's going on to do a good job.

7) If you use soldering flux, be *sure* it's rosin
based, not acid based. You need only a very tiny
amount, wiped on in a very thin film. A dab on the end
of your finger is enough for a whole DIY-WB circuit
board.