As TR1BAL said... you need to get Photoshop. It seems your skills are at an advanced enough level to be able to understand the program, and I'm sure you will be able to see a vast improvement in skill when you start to use it.
On the topic of your signatures, you need to wean yourself off c4d's... currently they dominate the compositions, placed haphazardly across the pieces, and eliminating all sense of flow. Try out the use of clipping masks instead, and attempt to further blend the stock in with the surrounding imagery.
As both Squidge and TR1BAL have said also- work on depth... sharpening what would be in the foreground, and blurring what would be in the background- defining important sections/features of the piece.
Lighting could be improved... define the focal by highlighting it more- and remember to look at the existing lighting then follow that when creating the light source, otherwise it will look completely unrealistic and not match with the shadows on the object/people.