my cacti always die. Try this: suck in your stomach. thats how my cacti look. tips?

I'd have to say either over-watering or under-watering... Got any pics to share?

probably over watering causing root rot. cacti don't do the "suck in the stomach" thing from underwatering until they are WAY dry. (like months). but that is for true cacti. if you have other succulents, their requirements are different and usually need more water, although not a lot more.