1. Write everything that you want without thinking about anything else, even word limits.
I work better when I just sit down and start writing without being interrupted. Write whatever comes to mind when you have time. If you like to write a bit and come back to it later, then it is no problem. By writing everything you want, you make sure that you can include everything important without skipping over something while your thinking about other things.
2. Pick and choose the most important points and work around it.
Bruce Almighty
When you are done writing and are satisfied with everything you write, it's time to cut it down. Similar to when a bush over grows, you want to cut it down until it meets the requirements. Cut out anything you realize you are rambling about (Trust me, there is going to be a lot).
3. Run it through google translate, especially if it's a story.
Google Translate is your friend. It has a limit of 5000 letters per entry but it works if you spot an error. You can work in small sections and still keep up. This is the part that helps me catch any grammar errors or repeating words I make while I am writing continuously.
4. Trust yourself (And everyone who helped you)
Shut Up Flower Boy Band
The end product of your words is your metaphorical baby. Don't be ashamed of it. There is times when you will hate it but you will be happy in the long run. I know that your nervous but you really can't do anything about it. Be happy and confident that others may benefit from what you wrote and at least take away what you put out there. And the people who help you make it happen are taking their own time to help you catch anything you missed.