First, if you're an intermediate or beginner English user. You may use a simpler word in your writing. The one that you are more familiar with. Have a translator site on the new tab or dictionary on your side. Don't feel down if you are not that good, at least you are trying to not making mistakes and keep learning.

Short of time to flip the dictionary pages?

Well, you can plug in some grammar checkers on your browser. I always recommend you to set Grammarly as your browser extension. Why? Because it's very easy to detect your errors and immediately suggest you the right spelling and sentence structure.

Reread your sentences again and again until you feel it's ready to go. If you still doubt it, seek for some bits of help from your acquaintances to check it for you. Different eyes see things in a different way. Don't underestimate your buddy.

Keep yourself settle down and chill. Don't rush when you are writing, otherwise, you are making trash. Your grammar will be messed up and need time to fix it. It's a waste of time. Try to write it slowly and put some passion into it. It helps to beautify your sentence.

Call it a day and continue it next time.

As mentioned above, don't rush. If you feel so numb and already about to die, go and have some rest, make yourself a cup of mild coffee. Who knows some new ideas will pop up in your mind while sipping your drink. Additionally, you will be more focused after some rest, thus more errors will be detected.

Improve your speaking skill because it's obviously related to writing skill. Other than listening to English songs and watching English movies, try some new things on the internet such as having an online class through Skype to improve your speaking skill. I would suggest Lingostan for this. It provides you the opportunities to speak and learn with a native speaker in your free time. It's so convenient.

So are you still thinking that writing with good grammar really needs a professional writing skill? As long as you focus on what you are writing and have a peaceful mind, you are good to go.

...and don't forget to learn from your mistakes. Improve yourself from time to time is the best way to succeed.

Goodluck.
Amer