I'll echo what Jeremy Eiler said earlier - it's finding the right target market. I can't tell you the times I have asked potential clients who they want to reach and they tell me "everyone."  I once talked with a new car dealer who told me that and I asked him if he really wanted to reach 13-year girls. "Well, no," he said.  Even McDonalds or Walmart doesn't target "everyone."

Identifying your target market as clearly as possible is key to a successful campaign