I applied and was successfully accepted in July. I applied several times over the last couple of years and was declined. Here's an excerpt from a post I made when I was successfully accepted.
"I wrote my application as is if it were a job application, I read through it several times checking for typos and rewording to make is sounded professional. I got an email and it was declined... AGAIN, but I read the advice given by the reviewer and acted in it... I narrowed my category down and found what I considered to be three quality sites.
My advice to those looking to apply... be straight and honest and as the guidelines state... write your application properly... remember, this is more or less a job and the application should be treated as such. Take time to read and FULLY understand the FAQ. Take some time to read the posts in this forum... all 130+ pages if needed... and if you're declined, look at the feedback, understand it and go for it again acting on the advice given."
As Jim says, read the guidelines, they are very thorough and choose a small category as there is so much to learn once you are successful, a large category would be overwhelming. Good luck with your application.
