Draw a rectangular shape at the start. A considerably big rectangular shape is required to make sure that you can draw rest of the stuff related to bus inside the rectangle. Remember you have to draw an outer shape of the bus so the interior is not to be imagined at all.
Draw two circles on the lower end of the rectangle that will look like the tyres. You have to draw the bus in two dimensional so you do not need to show the other two tyres. You are just showing one face of the bus; like you are watching it sideways.
Draw small squares in the bus at the top in a row. Give a gap between the first and the second square to differentiate between the driver’s seat and the rest.
Once you are done with your drawing. Just use the ruler to put the lines straight and erase the remaining part of the sketch.