Probably one of the most common mistake I see is when someone uses the wrong “There”.
There is a place. Try replacing it with “here” to test to make sure you’re using it correctly.
The dog’s toy is over there.
They’re is simply a contraction of “they are”. If it can be broken down into “they are” successfully, then the correct word is they’re.
They’re coming over tomorrow afternoon.
Their shows possession. You may test it by replacing it with the word “our”.
The kids are doing their homework.