I found that I had better success with clones when I cut them off with a pair of scissors and idmediatly chucked 'em in a cup of water. After I'd cut all I wanted, I'd take each one and put a 45 degree cut on the stem and then right back into water. I used to use peat plugs and a heat mat, but then I started putting them right into my hydro setup with those little round foam thingies. That worked really good, but I just had to make a spray clone-o-matic. If I lost one, it was because the spray nozzle had plugged up.
No matter what I did, the trick was not to leave the cut part exposed to air.