Dandruff is caused by a rapid turnover of cells so more cells are shed causing the flakes. Hormones may be involved as dandruff usually starts after puberty and it more likely to affect men then women.
TIP: First ensure that you actually have dandruff and not an allergic reaction to the Sulfates (detergents) and fragrance in your shampoo. Buy a shampoo without these two ingredients and use for 1-2 weeks to see if this is the cause of your flakiness.
Step 1 - Treatment
Look for a scalp treatment that has exfoliating beads.
Step 2 - Cleanse
If you have mild dandruff limit washing your hair to twice weekly and then use a 'frequent use shampoo for dry hair' which will remove the flakes and add moisture to the scalp. If you have severe dandruff look for bacterial inhibiting ingredients.
Step 3 - Conditioner
Use any conditioner that is recommended for your hair type. Do not place conditioner on your scalp.
Step 4 - Sunscreen
Studies show that the sun inhibits growth of the yeast that causes dandruff - Malassezia.