Well, this discussion might be specially helpful for beginners. I wanted to share what I learnt from my initial experience and some of my friends who are with DT for long time. During initial days many people might have sufferred to enrich his profile with lots of photos. At that time we do not understand why most of the photos get rejected although those have earned lot of good feedback from other photography forums.
So here are few tricks :)
Accept that buyers who visit your profile here are mostly looking for commercial photographs. So perhaps one of your photos has great life in it with nice play of light and shades or some blurred subjects. But people who are in need for commercial photos might not feel interested in that.
If your photos are getting rejected in submission phase itself then read what all points have been shown as the reasons of rejection. Open the photo again and understand the faults.
Prepare a self-checklist with all those points. Next time while taking a photo or editing the same match it against the checklist. Well, one does not have to carry the checklist always :) You can just recall them.
Sometimes I ask myself if I was a buyer should I buy this photo for my commercial/Editorial use?If the answer is 'No' then why. May be the reasons are poor framing,cropping of the main subject, noise etc?
If you have option to resubmit the refused photo then try correcting the errors and resubmit. Check if it works.
Now a days, all above points have become practice for me and they appear automatically before submitting a photo. Almost all my submissions get accepted.
Others might want to share their thoughts on this? :)
Here are few photos from my profile and others profiles. They are my favorite from this aspect.