Hi guys,
I presume this is a hard question to answer, since im guessing that you need to consider a lot of things to get realistic results.
But i would like to get some tips about photorealism and how to archieve it.
Do you mind sharing some knowledge with me and the rest of users? 
first you need a good model/scene with alot of details, then you need realistic materials/shaders/textures, then you need realistic lighting with a plausible camera
after all that you can tweak some final things in compositing to get the last finishing touches
Good models, textures, and lighting only goes so far. What a lot of people forget about making CG look real is that there are imperfections in the photographic process(digital or film) that just arenāt there in rendered CG. Cameras and lenses have a limited depth of field, there is an atmosphere through which the light moves, etc. A lot of this stuff is subtle and we often donāt even realize that itās there until it isnāt, and then our minds scream āFAKE!!!ā and we donāt know why. A good habit to get into is to use reference materials of the kind of thing you are looking to create. If you want to make a car, then look at how a car looks, look at how the light hits and interacts with the paint, how the glass on the windows has a different kind of shinyness to that of the paint, or the wheels, and so on.
Beyond that, well, a lot of the tricks and techniques that can be used to make something look photorealistic are very dependent on just what it is you are making, so I couldnāt tell you much more.