Some assume that the path to promotion is doing their current job well. However, promotion is about proving that you're capable of another job.
Hacker News commenter jrockway writes about his experience with promotions at Google:
The biggest problem I found with promotions is that people wanted one because they thought they were doing their current job well. That isn't promotion, that's calibration, and doing well in calibration certainly opens up good raise / bonus options. Promotion is something different -- it's interviewing for a brand new job, by proving you're already doing that job.
This is in someways the inverse of Charity Major's blog post Know Your "One Job" and Do It First. In her post she talks about knowing your "one job" and making sure you're doing that well before taking on extra curricular activites.
For promotion, therefore, you should know your "one job" and also the one you have an ambition for.