Is a home colon cleanse safe?

I know in general that a home colon cleanse is supposed to be pretty benign in terms of the harm it can do to you, but I really have no idea what I’m doing — as I’ve never done it before and have never seen it done — and so I’m just a bit concerned that I may wind up doing something that requires a visit to the emergency room. There are plenty of instructions that I’ve been able to find in books, magazines, and especially online, where there are tons of websites dedicated to this procedure and teaching you how to do it.