If you are visiting the coastal resorts in summer you will need light, casual clothing. You may need a raincoat while visiting the Black Sea coasts.
In inland Turkey you will be at higher altitudes so you had better take some warm sweaters for cool evenings and nights.
If you are visiting inland Turkey in winter you will certainly need woolens and winter coat. In the coastal regions or in Istanbul during winter you may pack slightly warmer clothes but a raincoat is a must.
In spring and autumn the coastal areas are warmer so you may take with you what the season requires. You may take your swimming suits too, since you may encounter some unseasonably beautiful temperatures. At higher altitudes you may need some woolens for evenings. if you are intending to visit the marvelous mosques of Turkey, there is an essential item for ladies to take; a head scarf. While visiting a mosque it is required that the ladies should wear a scarf covering their hair.
Also comfortable shoes are advisable for visiting archeological and historical sites, and sunglasses and sun hats are recommended in summer.