Help me to improve skill, pls!

If you are new to stock, you should consider these resources: https://helpx.adobe.com/stock/contributor/tutorials.html
Please read the contributor user manual for more information on Adobe stock contributions: https://helpx.adobe.com/stock/contributor/user-guide.html
See here for rejection reasons: https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
and especially quality and technical issues: https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html

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Hi,

I'm sure you can understand that we can not do a full Tutorial on how to get better photos, but there are lots of those out there on youtube, vimeo or other video platforms.

For this specific Image it maybe be that it has a to shallow sharp area and lack of sharpness overall. Try to look at other Photos of flowers and look for that kind of technical quality in your own photos.

Before you submit, please review the submission guidelines carefully and compare your work with other Stock inventory. To be accepted, your work should be as good or better than what's already represented in your keyword category.

https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html

https://helpx.adobe.com/stock/contributor/help/photography-illustrations.html
https://helpx.adobe.com/stock/how-to/tips-stock-image-acceptance.html

Hope that helps.

@Jill_C said it all.  There's nothing remarkable here.  It's just a snapshot of a typical flower.

If you really want to improve, enroll in some photography courses and join a local photography club.  Clubs are great for meeting people and going out on photo field trips together. 

Hope that helps.