I was in a meeting today, just doodling on my legal pad, and this guy was born. It's amazing to me that the simplest doodle might result in something appealing, and three hours of constant, concentrated work might not.
I'm always intrigued by what makes an appealing design concept and what doesn't. Better artists than I have spent their lives trying to crack to code. Sometimes, everything makes sense technically, but it still doesn't seem to gel.
When you're having trouble designing, don't be shy. Show people what you've come up with so far. Odds are, they'll be able to tell you what they like and dislike about your sketches, and you can use that information to find a design that works. Never underestimate the value of friends who speak their mind!