Many Turkish customs and practices are derived from Islamic practices. Etiquette demands that you wear modest clothing and remove shoes when visiting mosques. Women should have head, arms and shoulders covered, and wear modest dresses or skirts, preferably reaching to the knees. Avoid visiting mosques at prayer time or on Friday, the Muslim holy day. Note also that it's rude to point your finger directly towards any person, to show the sole of your shoe to anyone, to blow your nose openly or to do a lot of kissing or hugging in public.
Many women complain about verbal and physical harrassment in Turkey.
Although it's not necessary to be paranoid and let stupid hassles ruin your trip, it's as well to take a few precautions. At the very least, keep your torso, legs and upper arms covered, especially as you travel farther east. You might also consider wearing a wedding ring. When walking, look purposeful, ignore catcalls and steer clear of lonely streets after dark. Going out drinking by yourself is basically stupid.