I think the banhammer comes down on people who have a major flaw in their grammar that makes the article nonsensical. Or, someone who makes the same mistake over and over. I'll even use me as an example. I wasn't really proofing well. I've been warned once to clean it up or the banhammer was coming, so I made some changes in how I proofed. I should say that I backed off of CC for a month to get my frustrations out of my system. Sometimes, I still make mistakes, but overall I'm doing much better with my acceptances. I still get rejected sometimes, but I understand that it's going to happen.
So, n00b to n00b here are my suggestions:
1. Write what you want and what really inspires you and stuff that interests you. This eliminates that forced word count and you aren't just filling space that looks dull to the editor.
2. Walk away from the article for at least a day. Proof it after it's out of your head. First, this will help you find errors. Secondly, I find I can add about 100 words to an article in the proofing process. I charge $.10/word, so this is good for me.
3. If you get a rejection, try not to feel too bad. I hate rejections and that big, bold YOU ARE REJECTED stings. Don't go back to the article right away. Your frustration level is high and you're more likely to make even more mistakes. Let it sit and write another article. Go back and read what you wrote. Sometimes, after a second glance, I don't like the article anyway so I don't even resubmit. That's up to you, though.
4. Be picky about what public requests you write on. I write for public requests that are somewhat close to my per word charge (which is rare), and on subjects I feel will sell to someone else. I also don't write on just any public request topic, because I don't feel I can write and proof within a day. It makes me nervous to proof on the same day. I'm really bad at catching stupid mistakes.
Anyway, don't stress the rejection. I know some people have said they are cryptic. If you get a simple "you need to proof" then the editor probably found a really dumb mistake that you just need to catch. We all make them, so don't worry. You'll find the mistake when you go back and read with a clear head.
Also, I'm no literary genius, so I keep my articles very, very simple. I've seen some people complain about commas and semicolon errors and can't find them and get angry because they think they are right about the sentence. I don't do any grammar trick unless I know I'm doing it right. I don't use any semicolons in other words. LOL If I'm not sure a sentence is done right, I rewrite it. I stick to what I know, and it's helped me.
I hope this helps a bit!