Establish the kind of hat you want to draw. Go through magazines, hat stores and the internet for pictures to decide on the kind of hat you want to draw.
Draw a cube or a cuboid depending on the shape of the hat's crown using a light pencil. Show the 12 edges of the cube. Draw a circle on the base and top face of the cube. Connect these two circles with lines to form a cylinder in a cube. For a cowboy hat the circle on the top face is smaller than that at the bottom.
Extend a line from the middle point of the length to the center point of the face adjacent. Drop this line to the middle point of the width forming a triangle. This applies for a cowboy and fedora hat. For a bowler, draw an upward curve at the center point of the length and a parallel upward curve on the furthest point of the width.
Draw two curved lines at the bottom of the cylinder. Extend these lines across the cylinder. This forms the hat's band.
Sketch out the shape of the crown in a shading manner using the darker pencil. Insert short curved lines in areas that exhibit folds.
Erase the guidelines, the cube and overlapping lines that you had drawn using the lighter pencil. This will allow you to see the final sketch of your hat.
Position a feather or a flower on the side of the hat. These details depend on the type of hat. A cowboy hat does not need such details.