Follow The Rules
When entering a writing competition the first thing you should consider are the rules! I have judged many contests and the most common mistake that I see when judging a contest is entries that are not about the topic.

Understand The Topic
Contest organizers generally have a specific type of writing in mind. Usually they are careful to state it. If entering a 5-7-5 poetry contest, for example, understand the number of syllables requires and if there are any other rules such as writing about something particular, follow them.

Not Too Long
When entering a contest pay attention to the number of words required. Most contests have a specific number of words required. This is especially true for magazine publication since there is a limited amount of white space in a magazine. But it is also often true for online submissions since one can only read online for so long before screen tiredness creeps in.

Grab Reader Interest
Writing for a contest can be different from any other form of writing. Judges won't read a work from top to bottom if the work doesn't grab their interest. Yes, it's true, your work will be ignored if it doesn't capture the interest of the judge. So capture the attention of your reader as quickly as possible -in the first paragraph if possible.

Grammar Counts
Watch your grammar! Yes, that is important. Avoid spelling mistakes. Avoid grammar issues. No one wants to clean up your work (no, editors don't either) so submit a contest entry that is spelled properly and all the grammar mistakes are fixed as well.

Write A Winning Entry
Of course, none of this matters if you don't write something that will win. Understanding the topic and your audience is important. If writing for a western magazine, for example, study the genre. Understand the wild west. Understand how past successful writers in this genre have written well received books. And put your heart and soul into your words.

So to win...
So capture the interest of your reader quickly, understand the rules and the topic of the writing contest, pay attention to any word requirements and watch your grammar! With that you will put your best foot forward towards winning the contest. - Written by Gary Kirk, writer and judge of writing contests.