1. Proofread before submitting. I'm an ex-English teacher so I am very particular about spelling, grammar and punctuation. It's very frustrating to read articles, stories, etc., that have not been proofread. Maybe your submission would be accepted if you took that extra time to capitalize a person's name or type "had gone" instead of "had went".
2. Only include what is absolutely necessary. Writing more to make a paragraph or story longer doesn't make it better. A long description or conversation can be grueling when a few adjectives or sentences depict the same thing.
3. Make your characters fit their descriptions. If your character is a distinguished gentleman, his language should be impeccable. If your character, on the other hand, is a child from a farming town where children work the fields instead of attend school, the language should play the part. For example, the child wouldn't say, "I'm going to shoot those rattlesnakes." It's more likely that s/he would say, "I'm goin' t' shoot them ratlers."
4. The setting of the story is like a painting the reader can step into. Help the reader identify with the background and where the story is taking place by using clear, descriptive sentences. For example, not so clear: As I walked down the driveway, the moonlight shone on the gravel in my path. Clearer: As I walked down the gravel driveway, the moonlight sprinkled jewels in my path.
5. Only write when the words are flowing. If you have writer's block, don't force yourself. Relax, take a nap, meditate, exercise, take a walk or run. Whatever suits you to take a break from your writing project, do it. Next time you begin, you'll have better luck at putting the words to paper.