I found this article that I thought people might be interested in. This is about the most common English mistakes that people make. Yes, even native speakers! It happens to everyone, maybe because they are tired, in a hurry, or they just aren't paying attention. But sometimes it's caused by lack of understanding.
Why don't you review the article and see if you make any of these mistakes. Is there one that you consistently make? From my experience, numbers 5 and 10 are extremely common, and I frequently have to help students with these. Let me know what you have trouble with! :)