What suggestions do you have for buying a diamond?

What are some of the most important things to consider when you buy a diamond for an engagement ring? I always hear “know the 4 Cs” or something to that effect, but how do you really know what they are if you’re not even close to being a diamond expert? What should you ask your jeweler about the diamond when you go ring shopping? Anything else I’m missing here? Chime in with whatever you know or have heard about this…anything helps! :)