I would be careful about using my camera to take pictures of police forces. They may feel intimidated and decide to take your film roll or wipe the data in your camera. I would not recommend making it obvious that you are taking pictures in Fatih, especially in the neighborhood of Carsamba which is infamous with its extremely conservative residents. That's all I can think of. Other than these, I don't think there is anything more to what you would usually consider before clicking in a western metropolis like New York City or Dublin.
Just a few phrases in Turkish you may find useful:
"Cekme!" (approx. pronounciation would be "checkmea") means "Don't take a picture/shoot a video!"
"Fotografinizi cekebilir miyim?" is the polite way to ask "Can I take a photo of you?"
"Fotografimi cekebilir misiniz?" means "Could you take a photo of me?" , also a polite form of asking.
