A lot goes into making a game, and each game and designer has a different mix of focus and needs for their games. Off the top of my head we have: world building, rules creation, technical and prose writing, art, layout and visual design, feedback and iteration, promotion and marketing, and community support skills.
Collaboration and contracting are good ways to make up for weaknesses, but so is practice and patience.
So what are you best at? What are you working on improving?
Wow. What an ass