You can use a heat pad. For me, my heat pad is hooked to a thermostat so it regulates....If you can't find one..find a small heat pad and slap it to the side of your tank (works better if you have a aquarium tank). so that way it heats up from the side. Keep the temp at around 80-82. don't let it drop lower than the mid 70s.

I feed my baby pacman about every 2 to 3 days, i dump around 4 crickets in there...I use the T-Rex calcium/no phosphate 2:0 for dusting the circkets