Good textures are only one component in achieving realism – although an important one. But more has to come together:
Materials
Textures “only” provide raw substance, which has to be interpreted and translated into physical properties of a material. This essential job is done by shaders, which have to be set up and controled by the 3d artist. For this it really helps to know something about the physics of light, how it behaves in interaction with physical bodies. This is a very complex but essential topic and reading up on it is well worth the effort!
Lighting
Often underestimated. But just as much as often, bad lighting is the main cause of flat and lifeless renderings. Good lighting is an art in itself. Luckily there are many very good tutorials on this subject out there: Try Google.
Software
Not least important, the rendering software you use has to be capable of producing realistic results in the first place. Advanced techniques like Displacement or Global Illumination should be pretty much standard by now but are still not always supported.