A trick to get the hinge on a glass cover?

I find that if the edge of the glass is wet, the hinge usually goes on easier but this does make the glass harder to hold.

Are you sure you bought the right hinge size? It is sized for the proper glass thickness, usually 1/8" thick for smaller tank sizes and 3/16" for larger tank sizes.

I put cooking oil on them and slide it from one end rather than from the front.

Yeah, it's the right size. 1/8 inch for a ten gallon canopy. My daughter with the strong hands got the hinge on. I tried water but didn't think to try cooking oil.