Before applying for Google AdSense, make sure that you read all of Google's terms of service, policies, rules and guidelines. Also make sure that you're following all of these rules because otherwise you will be disapproved.
If you're trying to apply for AdSense via HubPages, you first have to make sure you have lots of hubs written before applying otherwise you'll be disapproved for insufficient content. Google appears to be stricter now in approving people so there are many who keep getting disapproved. I also got disapproved by AdSense for insufficient content when I applied because I only had 11 hubs at that time. Now I'm planning to write more before re-applying.
If you check the HubPages forums, you'll see that there are also many who still don't have AdSense and were also disapproved for insufficient content. Some who recently got approved for AdSense said that you'll need something like 25 or so hubs before getting approved and that you might have to be here at HubPages for at least a month or so. Hope this helps.