Startups are like real time schools that gives you learning experience at each and every process. Below are some skills that I am experimenting with these days while running Truffle.
Coding
Chances are that no matter what your idea is, it will involve some kind of web presence and for that you'll need to code. I always been a back end developer mainly coding in Java and Python but since there was no one in the team that knew front end I jumped in and started doing developing our front end, the interim result is not bad. Truffle.
Event Organizer
Again this depends on the nature of the business that you are running but chances are that you'll need to organize some promotional event that will increase your outreach to the customers
Marketing
In the past one year, I started from knowing just Java to steering a team of 5 people together towards a vision, building a relationship with my users, knowing some of the smartest people, getting my proirities right and making sure I am building something that has a need. This is not bad for a year.