I found that the main key is quality more than anything else with acceptance shots.

Make sure the image has a clear point of focus, do not crop or resize, shoot at the lowest ISO, avoid heavy shadow or high contrast shifts, and if in photoshop if you need to do anything more than a slight tweek then that image should not be part of a submission

A stock image is often used as a part, a design element, so you are the photographer not the artist in this case, if the designer wants a crop they will do it, do not try to provide the finished shot, think of copyspace and allow some space around the subject, the key is also to keep it simple.

My images included animals, people and objects, none were "shot for stock" as such but were selected with the above rules and I had 8/10 first attempt.

Someone said "Why Bother", I was refused at the first site I ever tried, in the 30 day wait I trawled the forums learned the process, got accepted at other sites, when the 30 days were up, I submitted again and was accepted, I never uploaded to that site after reading about them in the forums, I bothered because they had refused my images, and accepting that would have bugged me.

I went and uploaded to 8 sites but now I am only uploading to one, the one which gave the best consistant return oer 6 months, with a small portfolio.

David 

I do agree with steve's comments, and they are valid going forward, however we are talking about acceptance images.

One problem I have seen is new submitters "shooting for stock" trying to re-create a top 50 image, or something they saw in another portfolio, looking for the special thousand download image, rather than shooting simply for acceptance, where IMHO quality is the main issue, I have never cropped or made an image "Pop" for acceptance, and have always been accepted first time except the very first site, with quite boring images, so I can only speak from my own experience.

The cropping issue and doing two images sounds like a good idea after acceptance, as is testing how far you can go with post process different sites different rules.

The two bits of advice I took early on from the submitters was "keep it simple", from the designers "don't crop".

These are only my observations on initial acceptance.

B.T.W. several designer said in another forum, that many a sales was lost as a lot of the image are already over cropped, and they have had to settle for thier second choice

David