Are there rules for designing coats of arms?

As title says, are there?

I am a hobby writer and have a couple instances where I´d need a family crest or coat of arms. What symbols can or should be on a coat of arms, what colours can be used (and how), how is the coat of arms used, really anything to know to go about making and designing one to look "real". Alternately, how about a family crest? (above questions apply) I´d assume these two go hand in hand.

A list and short/easy to understand explanation would be greatly appreciated as well.

Sorry if the flair is wrong.