Lather up with a shampoo that promotes straight strands or zaps frizz. Most formulas will have "sleek" in the product name. Rinse it out. Follow with a conditioner in the same product line and rinse with cool water.
Apply a frizz-fighting serum to damp locks. For thick hair, use a nickel-sized dollop of serum; fine or thin hair needs a dime-sized dab. For super curly hair, you can also spread on a light coat of straightening lotion. Squeeze only a dime-sized amount into your hand, if you're using a frizz-control serum. Spread that evenly over your tresses. Run a wide-tooth comb through your locks, to distribute the products evenly and unfurl any knots.
Pin back the top sections of your hair using plastic clips. For stick-straight strands, you'll need to blow dry in sections.
Place a large round brush under a two-inch section of hair and blow dry, pulling hair out and away from your face as you go. Always keep the nozzle of the dryer facing downward onto strands, to prevent frizz.
Repeat Step 4 all over your head, unclipping sections as you work your way around your hair. All of your hair should be completely dry, before you flick off your dryer; any damp sections will get frizzy or wavy, if left to air-dry.
Lightly mist a heat-protectant spray onto your locks.
Take a two-inch section of hair and pull it away from your scalp. Run a heated flat iron down the section. Keep the iron moving over your hair; holding it in one spot too long can burn the hair shaft. Use one fluid motion to sweep the iron from roots to tips. Repeat until all hair is ironed.
Spritz on a light coat of hairspray to lock your style in place.