Knowing if we are a good language learners is not an easy task. That is why the best way to assess yourself is by asking questions and analizing your own answers. Try to be as hones as you can, as these lines may be a good guide for beginners.
It is worth asking yourself questions such as, "What are some of my fears and apprehensions about learning English?" Write them down and then check them out with other learners to see whether or not they are justified. While learning English, spend time interacting with positive language learners -- those who are enthusiastic about learning English! Hopefully it's catching! Also spend time with American friends who by nature are encouragers -- those who continually make you feel good about your level of English. Think about what your personal strengths and abilities are as related to language learning -- both personal character traits as well as natural learning strategies.
"Do I believe that the content of the course will meet my needs for life and work in England or in the U.S.A.?" Few learners ask themselves this extremely basic question. And if the answer is negative, then it is imperative for you to get hold of a copy of 'English Step-by Step' (or something similar) in order to supply you with the everyday words that you will be needing for handling daily living needs in England.
To find out about the textbooks used at your school, ask other students for their comments and opinions. If you discover that the grammar explanations are not clear enough, borrow a copy of S. Suarez's 'A Practical English Grammar' (published by Harvard University Press in Cambridge).
"Are my teachers stimulating to be with -- or is a particular teacher's teaching method frustrating me?" Then...