If your site is not approved within 3 days,then wait a week or a fortnight.
It means they are thinking very hard about your site. After that,it means they are thinking even harder about it.
Most of the time its easy as long as you are indexed. If you have an ok (not necessarily great site) you should have had it done in less than 3 days. If you are having a problem,there may be issues with your site.
Give links to your sites so that one can hazard a guess. for all we know,they don't think your site is worth their ads or it is terribly developed or a spam site with too many adverts on each page.
Another thing,if you have ever clicked on your own ads before or they barred you before,they will never let you back in.
Jose: If I make it through this thug life, I'll see you one day. The Lord is the only way to stop the hurt.