there is a whole section here on this topic, called CPA. Inside there are about three sticky threads outlining exactly what you need to do to get accepted, written by people who know whats up.
But since here we are anyway, I can tell you the biggest thing people fuck up is fluffing up the application. Here is how I got accepted into every fucking one I applied for the first time I tried when I did not know shit:
1- create a blog about internet marketing and make 5 posts. in the 5 posts talk about different ppc platforms and what you like / don't like about them, here are some to talk about...7search, bidvertiser, looksmart, miva (make sure you say miva sucks in your blog or they will know you are not in the game) adknowledge (mention how expensive they are) and post how you are just starting to get into ppv.
2- in one of the pages post your real picture and say something like "My name is xxxxxx and I love advertising online it is my passion and I am getting better every day, I have been marketing online for just over a year and have come so far, welcome to my blog, if you see something you like please post a comment!"
3- on your application check NO on the question about if you use incentives. Also put this exactly into your application where it asks what you do for traffic
"I like to use PPC to drive targeted traffic to relevant offers and match the demographics of the audience to the offers so I can maximize my conversions. I am in the process of building my email list so I can have a long term asset of more targeted traffic. I am relatively new to the CPA space only one year in, but I am determined to become successful with your network"
Use that or something close and don't bullshit on your app. These people are going to know you are full of shit. If you are a noob, say it, but make sure you know the game and the terminology.
3- submit your application during THEIR BUSINESS HOURS NOT 3AM and as soon as you submit CALL THEM IMMEDIATELY and tell them "I just submitted my app and I wanted to call and introduce myself and see what I can do to help the process along" if you don't do that step don't come crying to me because that will get you accepted 99% of the time and if you are too scared to do that than you need to find another line of work.
Best of luck, remember, CPA section, top 3 stickies, you will succeed.