The most common mistake writers make is not reading the contest rules completely. Most contests have a topic and the organizers of the contest have a specific idea of what they are looking for. As an author you should carefully read the contest announcement and try to understand what the organizers are looking for. Don't try to fit your pre-written story or book into a contest that you find. Rather, write something specific to the contest. Write it with a clear idea of what you think the contest topic is.
Proper grammar is important! Read, correct, read again, and make corrections again. Use a spell check to be sure that every word is spelled correctly. Proof read your work and ensure that you have removed any issues with grammar. When you are finished - don't submit your writing. Let your writing sit for a day or two before proof reading it. That means you can't wait to the deadline day to write and submit your writing. Give yourself plenty of time to create your contest entry, proof read it, and submit it. If possible have a second set of eyes look over your writing. Sometimes the most glaring problems aren't noticeable to a writer on the first day but may be to a second pair of eyes or after you've let it sit for a period of time. Let the writing sit - move on - and come back to it with a fresh head.
What are the contest requirements contest on length? Most contests do specify a maximum and minimum required number of words. Word processors usually have word counts built in. Take advantage of that feature and be aware that many online word processors simply aren't that accurate.
Writing posted online is formatted differently from writing posted in traditional print. When printing a book white space costs money. That's not the case online where there is no cost for white space. So when posting writing online words are not indented. Instead of indents an extra line space is added between each paragraph. That is different from the printed text. Understand what the requirements and if not specified you should follow the following rule. If you are submitting your writing on the website (using a form) or emailing it follow the online formatting requirement. If you are placing your writing in the mail and sending printed material we recommend the traditional approach for printed material.