When you're writing, you don't have facial expressions or hand gestures to help get your meaning across to your readers. Because of this, you should be careful of your grammar. I realize that we're not all English majors or something, but that doesn't mean we can't write well.

Here are some common grammar mistakes to get out of your story:

Your vs. You're
     Remember, your indicates possession or ownership. For example, your ring, your jacket, your house. 
     You're is a contraction meaning  you are. For example, you're moving, you're washing the dishes, you're fighting the dragon. 

Their/There/They're
     These are easy to confuse. Their, like your, shows possession. For example, their home, their baby, their castle.
     There indicates a place. For example, they went there, the sword is there, there is the cave.
     They're is a contraction meaning they are. Examples: They're leaving, they're dancing, they're going to the beach.

Were/We're
     This is just a matter of punctuation. Were = past tense of are. For example, you were coming, they were here, we were fighting. 
     We're is a contraction which means we are. For example, we're going to the store, we're not coming, we're in trouble.

I hope this helped. Thank you for reading, and let me know what you think! :)

-Ash-