The most important thing is that you show them that you know your stuff. There are many people who have no clue on how they will promote CPA offers and then simply try to join networks to turn them into "testing tools". It's obviously not good for the networks, because this type of people usually generate a lot of work for the affiliate managers and give very little return, without mentioning the fact that many of them end up using illegal techniques.
So it's important that you show them that, although you don't have great experience and earnings to show, you have a well defined strategy and know what you will do after you get access to their offers.
Also, you may want to consider to get started with smaller (not new) networks and then join the big ones when you have some income proof to show them.