Having been in a startup that got accepted into the 500 Startups last fall, but also got turned down many many times before from VC's and other accelerators, here's my advice:
Obviously accelerator programs are meant to influence startups that are growth oriented. They may or may not be interested in your space, however it's your job to give them a reason to be. One good reason is metrics that not just meet the number they told you to hit previously, but metrics that STAND OUT. The metrics that will get investors and accelerator programs interested in chatting are the metrics that spell exceptional traction that's proportional to the time you went live. To be more clear, each year it will be harder to do just that. It's not impossible though to do research and listen to your users to make changes that will enable you to have a breakout year. I know this because our app went from 10,000 users to 250k users in less than 3 months.
Secondly, monetization strategies are key. If they see awesome opportunities for you to make money and you don't, they'll want you to figure that out first. If you have one or two, prove that you've been testing those strategies by either a) learning from your mistakes or b) growing capital. They want to know that their money is not the only money that will come in to your business. They want to see you work for it.
Lastly, the most important piece. The piece that probably weighs 2 or 3 times more than anything else i mentioned, which is your team. They will google, research, and talk to others to know more about you and your founders. Make that information transparent as possible before you sit down with them. It's not bullshit when they say don't reach out to individuals in their network to vouch, because normally, they won't have to vouch. Accelerator's don't invest in ideas, they invest in teams that can take any idea to the next level. Teams that can do that have chemistry while working together, same visions for where the product or idea is going, and established track records of doing so.
Hope this helps, and good luck.