After you submit a design or art print, you'll see a banner above the submission with a green "ask for feedback" button. You can use this option to ask the Minted Community for critique and feedback on your piece. Your request for feedback will then appear as a comment on your design and in the rotating banner at the top of the challenge gallery. And don't forget to give back by offering feedback on others' designs! (more info here)
Pro tip - BE SPECIFIC! Designs that include direct questions generate many more responses than designs that say "feedback welcome", or "how can I improve this?". Hone in on those details you’ve been agonizing over! Focusing on one element of the design at a time (like color, typography, layout, etc) makes it much easier for others to give you feedback.
You can find more tips on how to get feedback on your work here.