Here are some of my works. I just got back into G&A, so its nothing super fancy. I'm open to any comments, as long as they are constructive
The effects are over the top, text is badly placed, in 1 and 3 the flow is bad, in the second one the focal is blurry and there is a border piece near the top that doesnt wrap around the whole piece, the use of c4ds is overdone, the renders are not blended in to the background really at all (with the possible exception of #2), lighting is not really consistent. Work on text placement (in most cases do not align text to corners or at the very edge of any side), blending (try make the render look natural in the background), flow (make the lines in the image align to a certain point or direction, as opposed to conflicting directions, such as in #1), lighting (make a consistent lightsource, with accompanying shadows and reflected light), subtlety (to quote miraj, simplicity is the ultimate sophistication, try to keep it simple but interesting, rather than bright and glaring). Check out some tutorials, they are very helpful.