there is no single way to aproach "realistic" style.
"Realistic" style is simply applying natural looking lighting set ups. These can vary wildly, "Realistic" is completley dependant on the ambience you are trying to convey (indoors with neon lighting, outdoors in the middle of the day...ETC) so...basically, just observe real samples of the real ambient you want to recreate, and express your observations as faithfully as you can in your art.