Types of moves are a bit different, but more important, than what type the Pokemon are. I currently have a team with the following types represented:
Water, Fire, Grass, Ice, Electric, Dragon, Steel, Ground, Poison, Normal, Ghost, Bug, Psychic and Dark
However, my pokemon cover only these types:
Grass, Water, Psychic, Dragon, Flying, Dark, Bug, Steel
Be as diverse as possible in your move sets is the best advice. No more than two moves of the same type on your entire team, and no more than one move of a type on a single Pokemon.