There’s tons of list of ‘things to focus on’ to be successful.
but this one is really excellent (well, it seems excellent, we’ll try and let you know!):
http://www.paulgraham.com/13sentences.html

And because I’m all for brevity, here’s my condensed version:
1) Deliver to your users. Bring something valuable to them, listen to them, serve them well.
2) Adapt constantly. Launch often, accept to change your initial ideas, test and measure.
3) Keep it lean. Don’t over spend, don’t over engineer. You know what’s great about being ‘good enough’? Well, it’s that it’s good enough…
4) Monitor goals. Pick up meaningful metrics, and mind them constantly. They are the only objective and quantitative measures of your success, so do really focus on them.
5) Don’t give up. Success is always slower to come than expected. Bad news happen. Investors or journalist may not ‘get it’. Deals will fall through. Just go on.