If you've ever been in the middle of a fiberglassing session and had your epoxy resin suddenly start smoking as it rapidly became hard as a rock, still in the cup, with your glass cloth not yet applied, you will like this tip.

Tape a plastic cup into a bowl, then mix your epoxy in the cup.  After it's well mixed, add some ice around the cup to cool the epoxy.  The will guard against hot spots from forming in the epoxy which can lead to a runaway situation wherein the epoxy cures at a very accelerated rate.