It wasn't clear to me, is Ruby the first language you've learned? How many mini-projects have you tried, to see what you're capable of? You're better off starting with such projects, than leaping into anything big.

Versatility is important. Try to do many different things in your programming. Even if you don't like some problems, think about how you'd solve them.

At a startup, you'd be one of few employees so you could have many different tasks given to you. If you have experience or gut feelings on how to approach several problems, you're more likely to be able to jump in and not take time flipping through manuals.