1) If your teeth are feeling senstive, then reduce the frequency of use. Try every other day, then drop to once a week. Then finally drop to use once or twice a month to maintain the effect.
2)Buy yourself some special toothpaste for sensitive teeth- it basically fills in the porous surface of the teeth that is making them sensitive.
3)Red wine, tea and coffee all stain your teeth. You must avoid drinking any of them for at least 4 hours after using a strip or the colour goes straight in to your teeth.
Using the specil tooth paste i mentioned should help stop your teeth absorbing so much.
Hope that helps.