Some boards I'm building have tiny 16-pad 3mm x 3mm QFNs which I am hand soldering.
I've found a method that works for me:
Use tacky flux and build up some solder on the PCB pads, taking care not to get too much on the centre pad.
The use a hot air gun to heat the component and board together and tweezers to drop the QFN onto the molten solder pads.
The flux ensures no solder bridges.
It works well for me, but I was just wondering what other methods you use?