Pedantically speaking, there is no such thing as a family crest. The total image itself is called a Coat of Arms. The "Crest" refers only to the design that sits right on top of the helmet, which sits on top of the shield. A Coat of Arms is the total design of a shield with a design and a helmet crest. Also, they are awarded to individuals; not to families. However, an individual can bequeath his/her coat of arms to sons and daughters for their own use. This is common. A good design follows all of the rules and guidelines for coats of arms regarding colors and charges. Also, the simpler the design, the better. Charges on the shield or crest that have a literal meaning are better than those with a symbolic meaning.