This means to pay attention to how you use English. Think (a little) about how you are going to say something before it comes out of your mouth. But don't think about all of the problems you have in English at the same time. Just choose something your know you are having difficulty with and work on using it correctly. For example, if you know that you have problems remembering to use a, an, and the, spend a few days trying to put them into sentences as you speak. Don't worry about anything else. Concentrate on that. When you feel that you are improving, choose something else to work on. Just keep trying and little by little, your English will get better everyday.