First of all, use Yafray for that kind of stuff. Second of all, it seems that you’ve created your glass out of primitives, try the following technique:
Add a plane.
Now delete all vertices but one. Line it up the grid (shift + s -> selection to grid) and extrude one by one as I did in the screenshot.
Now select all vertices. In the MeshTools tab, change “Deg” to 360 and press the spin button. Spin the mesh from a top view and be careful to place the red-white cursor-thingy as I did in the screenshot.
Smooth the mesh and add a subsurf modifier.
Now box-select the vertices which were doubled through the spinning of the mesh and remove doubles (also MeshTools tab).
Now let’s get to the material. Make sure you choose Yafray as renderer in the render scene tab.
You may now choose “Clear glass” as material for you glass. For the extended render settings google for Yafray tutorials and have a look at my .blend.
There are probably better glass tutorials out there, hope that helped anyway.