This a image I just created. As a beginner, how can I improve?
Practice, practice, and more practice. Through practice, you’re not only improving your skills, you’re training your eyes so spot mistakes. Right off the bat, I’d say you should move your camera back, and take a look at proper photography composition techniques. Essentially, as 3d artists, we are attempting to approximate real life. If you can get that camera positioned right, that’s a large part of the issue right there. Lighting is the next big step. Again, you want to try to approximate real life. You can find lots of diagrams for studio lighting online. Also, check out Andrew Price’s tutorials over at blenderguru.com. He does a really good job of showing you how to achieve simulated realism.
As to the models and texturing, I think you did pretty well over all. I’m seeing a lot of errors in the cup’s lid. I’m not sure what those dark bands are, especially since you have the face shading set to flat (you need to switch that to smooth). Normally, I would suspect that the bands are due to stretching out the normals. You would fix it by adding controlling edge loops close to the angle changes. That only happens with smooth shading though.
The texture on the cup is also stretched vertically. You either need to make the cup shorter to fix the image’s aspect ratio, or remap the cup’s UV.
I see you’ve also used the focal length on the camera to get a blurry background. I would recommend turning that off, as it’s a dead give away as to the origin of the image. It looks pretty fake. There is another way of achieving this effect through the use of compositing nodes, along with the z-depth of the camera. I believe you’ll find a tutorial on the subject over at blenderguru.com, but if not, there should be many on YouTube.
You’re off to a great start, and you’ve accomplished many difficult things in your project, not the least of which is UV mapping and texturing. Good job on that. Just to reiterate though, always be mindful of the image’s aspect ratio in relation to your object. A stretched image is the best way to ruin an otherwise perfectly good image.
Oh, and remember to practice!