Between 23.00 - 07.00 consider to take a cab as well. Taxi rates here is the cheapest in all over the world.
The tramway is cheap and easy to use. It's the fastest way to get around during rush-hour traffic and it's above ground so you get a view of the city. But don't miss a ride on a ferry boat; the view of the old Ottoman architecture from the Bosphorus is breathtaking AND they sell snacks.