|Hi Alexander, greetings from the Critique Club!
Regarding your shot:
I believe that you didn't quite consider the background when shooting your photo. If the emphasis was to be given to the roses, then both the bottom right element and the top one out of focus shouldn't be there, they distract you of the foreground. When composing your photo, get accustomed to sweep the viewfinder clockwise to check all the elements. Think of what you want to communicate and then compose accordingly.
Technique / Lighting
The photo is a bit dark, a greater aperture should help this, and the stem of the rose would be green instead of nearly black.
Nice sharpness, and you could have made use of the full 800px size limit, it's smaller and for that you lose impact.
As a side note, please don't forget to include the EXIF information in your photos, your previous ones had it, but the way you saved this one stripped the image of that information, and that is a vital part of the image validation rules (at least for the original files).
Steadily you're building your average score, and if you remember a few basic rules, than you just need to use your imagination.
If you have any questions feel free to contact me.