Good question. I struggled with that for over 8 moths when I finally broke through that threshold.
If you're talking solely about earning through Hubpages, then I'm sorry, but it's going to take a long, long time.
You will need to have a good number of hubs online, at least 60-100, with good search engine ranking. This along is a mammoth task, one that isn't for everyone.
On the other hand, it's actually easier to make money with your own website, and a whole lot more too.
Write unique content, build backlinks, and keep writing unique content - you'll be earning a lot of $$$ within a few months itself.