If you can, always allow your hair to dry naturally first as this reduces having damage from both the hairdryer and the straighteners. Using a heat protection spray on damp hair is a must. A hairdresser once told me you can always tell when someone straightens their hair a lot from someone who only does it occassionally simply from the extent of the damage....theres no getting away from it Im afraid.....you can just limit the damage with spray.
Try getting a Tanagra treatment - it has made the condition of my hair loads better (I have mine relaxed and coloured). If you Google Tanagra it should give you a list of hairsalons that do it