You get a GST cheque if you have a job, make money and file for it with your taxes. If your not getting it, then you either;
1. Owe the gov some cash, you made too much and they want their share.
2. Forgot to check that little GST cheque box on your tax return form... dummy. tsk tsk.
I would suggest sacking the person who did your taxes [if that's yourself then run your crotch into the corner of a desk or counter].
The more money you make the more money you get back for GST. I believe there are several tiers, it is not a continuous function in the sense that if you make $10 more than last year than you should get more back in GST.