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Wash your hair first, then pat it dry with a towel. Hold the hair dryer above your head, and aim the nozzle down at your sides as you blow dry your hair.  Set the style afterwards with some hair wax. Add a flat, wide directional nozzle to your hairdryer to make the process more effective and give you more control over the direction of the air flow. There is no need to wash it more often than that. Not only can over-washing affect the texture of your hair, but it will also remove any styling products that you applied to the sides. If you remove these styling products, the sides will poof out. Not only can they look stylish and keep you warm during the colder months, they will also help keep down the sides and prevent them from poofing out.  Make your hair look longer by parting it down the middle before you put the hat on. If you don't like wearing hats that much, try leaving it on for about 2 hours; after you take it off, your hair should be flatter along the sides and not so poofy. Rather than combing your hair back, try a middle or side part instead. This works best when the sides are still short, but you can use this technique after you've flattened the sides with a hairdryer.  If the sides of your hair are starting to get long, you can keep them flat by applying some hair gel and using the palm of your hand to smooth the gel downwards into your hair. Use the handle of a rat-tail comb to make the parts nice and neat.
Blow dry your sides down to prevent them from poofing out. Wash your hair every 2 to 3 days. Wear caps and beanies as an alternative. Change up the way you part your hair to conceal the sides.