This protocol is designed to help express proteins which require molecular chaperones in order to express well. The idea behind it is that shocking the cells at 42oC stimulates the overproduction of GroEL and other heat shock proteins which are then present in the cell to help fold your protein as it is expressed.
Grow your cells at 37oC to an OD600 of 0.3-0.4.
Have another incubator ready at 42oC and transfer the flasks to that for 30 minutes
Move your flasks to an incubator at 17oC, adding the IPTG (I used 0.2 mM) and letting them be for 72 hours. One way to do this efficiently is to start on a Friday morning and harvest on Monday.
It is worth doing a time course to see how long gives you the best expression - most people were very surprised to find that there were still cells alive and expressing after hour 48, but that's when I had the most protein made.