An alternate headline for this post could be, "Think for the job you want, not the job you have."
One of the best ways to make yourself invaluable and worthy of a promotion is to make your creative director's job as easy as possible. How do you do this? By thinking and working beyond your years.
When you get an assignment, tackle it as a team a level above you would. Take ownership of it. Solve problems before you see your CD rather than looking to them to solve them. An example of how to do this: "The client had concerns about X, and here's what we think is the best solution. What do you think?" An example of how not do this: "The client had concerns about X. What do we do?" (There are times when the latter is perfectly acceptable, like when you truly don't know what to do or there's a problem you don't know how to solve. If you already knew everything, you'd already be the CD. Because clearly CDs know everything.)
This may sound obvious, but trust me, saving your CD time by being a problem solver will get you noticed. And probably promoted.
A word of caution, however: do not overstep your bounds. This advice applies to your thinking, not to granting yourself authority you don't have.