If you don't get many surveys it can be difficult to earn much, crowdflower is one option which could up your earnings pretty much but it varies what tasks are available
Your best bet to earn more is to get direct referrals which in turn some of those may also get direct referrals etc which can give you a good income, especially if you upgrade your account. Of course this way costs money initially, it may also take awhile before you figure out what pays, sometimes you may lose out and other times you will gain.
Just so you know, I can not afford to invest out of pocket so I try my best to get referrals in other ways which is difficult. Reinvesting earnings elsewhere etc, best of luck