If photo realism is what you're looking for in a render.There are 4 aspects to it:
1.Model- go as detailed as you can .. round the corners and edges, make sure there are gaps between objects so no clashing between objects.
2.Lighting. Make sure light source is balance. Try not to do much dummy light. let every light come from a pre-defined source, say window, lamp, etc. Unless you're doing a studio render, decide which time of the day you like to project in your scene.
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Materials- In reality, all materials has some degree of reflection. leaving one without reflection will make it dull.- Be conscious also of your mapping and texture scale.
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Vray settings- try to go higher settings (not the default) add Ambient occlusion and use the in-built color correction tools in the vray buffer.
It will greatly enhance your image if you use photoshop. Even the best of the best in visualization use these tools.
Invest time in reading the manual and do tests yourself. you'll be amazed at what you can discover.
The easier way though is to download some render-ready models. and see the settings. You can even grab the materials that you like and include in your library.
these are the basics but there are hundreds of parameters you can experiment on.