I use a helping hands to hold the board nice and level, then place the chip carefully on the board square on the pads. Then I gently touch the iron to the exposed part of the pad (which is much longer than the pin resting on it) and touch solder to the junction between iron and pad so that it flows onto the pad and up onto the lead. Sometimes you bump the chip, and sometimes the surface tension of the solder pulls the chip around a bit, so you might want to clamp the chip to the board; the heat sink clamps Radio Shack sells would work. I never bother, since it's easy enough for me to use tweezers to adjust the position of the chip if necessary. Let the chip cool a bit after the first joint, since it usually takes several seconds, and the limit is often as low as about 5 seconds depending on your iron's temperature.
Once the first pin is soldered, the rest are easy.
The advantage of this over Ivan's method is that the chip is nice and flat on the board. A combination method that shares this advantage is to tin just one pad, then use tweezers to place the chip while you heat that pad. Once you've soldered all the other pins, I'd go back and put a bit more solder on the first one to ensure that you don't have a 'cold' joint.
When the chip is soldered down, clean your iron and place the tip sideways along the chip pins so the tip touches all the pins at once. Any excess solder will cling to the iron so you can take it away. If you bridge any pins, this will usually clear the bridge. If one pass of the iron doesn't remove a bridge, don't try again; instead, use some desoldering wick to clean up the bridge, or add some liquid flux before trying the iron tip trick again. The iron tip trick only works when there's plenty of flux remaining.
