If you’ve already used up the 5.5GB of space you can easily get for free, you need to start using referrals. Dropbox give each user a unique link, which you can get at https://www.dropbox.com/referrals.
Anyone who signs up through this link and downloads the app on their computer will earn both you and them 500MB. As we know, Dropbox is great, and free, so recommending it is not difficult.
I would advise starting with a message on Twitter and Facebook, if you’re on these networks. You can do this directly from https://www.dropbox.com/getspace.
You can also add the link to your email signature. Something like:
‘I use Dropbox – sign up via http://db.tt/yourlink to get an extra 500MB free’
As a special offer for anyone who buys the Dropbox Essentials book, we will have a Dropbox signup link on the front page of www.DropboxTips.com. This link cycles through our readers’ unique links, so that anyone who signs up via dropboxtips.com will get an extra 500MB, and earn one of our readers an extra 500MB as well! If you’ve purchased the ebook , you can add your Dropbox link at www.dropboxtips.com.