In this tutorial I will show you how to create two common glass types. The first type will be a generic wine glass while the second will be a squareish type.
In the Front View create a line that matches one half of the glass shape. It can be like the one you see in my picture or you can use a different shape. Some things to keep in mind: a) create both the outer and the inner surfaces of the glass; b) the vertices in the yellow rectangle should have the same X coordinate (preferrably 0); c) the vertices in each of the green rectangles should have the same Z coordinates (this will ensure a smoother center of your glass; d) use smooth and bezier vertices, because corner vertices will give you rough geometry.