Before we start to drawing this picture we need to set the image of glass in the mind that how it looks like we should make the sketch of the glass in our mind. And from which point should i need to start which will be easy for me .So let's see a look towards the glass which is given in the below.
Now set its vision in the mind and and start its painting as like the vision in the mind from which point it will be good for make. In the glass picture you can looks like a oval types of shape in the side angle. So for a glass picture it you should make its oval in the top as shown in the picture below.So let's stats from its oval
Draw a flat types of oval as shown in the picture in the above from the arrow point and then move towards below and then join in the starting point with curve like u shape in the side of oval.
And then draw a line which will not be straight it should be just cross type towards below from the start no.1 point as your size you want to make .
Make another as same type in the opposite side as given in no.3
Then connect the end point of no.2 and no.3 with a curve to finish it. And now you are ready for color.
Then you add your choice color in it to look it natural. And your painting is now ready.