Attire - What is the look that you're trying to achieve? Do you want to match your suit with a hat? Formal attires require formal looking hats. Fedora hats go well with coats and ties because they are structured. If you want to look stylish in your summer attires, choose hats that are less structured and made from light materials like straw.
Size and proportion - Large hats are best worn by tall men. If you're quite short, hats in smaller sizes will be the best option for you to wear.
Face shape - The four basic face shapes are heart, oval, round and square. Use the following guidelines according to the shape of your face.
a) heart - medium-sized and wide-brimmed hats
b) oval - hats with moderate height, tapered crown and a moderate width brim
c) round - hats with medium height and full crown
d) square - hats with curves and rounded edges
Color - The color of your hat should match your outfit. However, this doesn't mean that your hat should be of the same color with your shirt and pants. Just make sure that your hat's color complements your clothes' color.
P.S.
Here are some terms related to wearing your hat.
a) Don your hat - Put it on.
b) Doff your hat - Put it off.
c) Tip your hat at the ladies - Grab the rim of your hat and lift it up slightly. This also means grabbing the rim of your forward gently.
d) Grab the crown of your hat. - Grab the your hat by its top part.
