Re: Looking to take the CELTA
Welcome to the forum, M.A.U.
Jim Scrivener's Learning Teaching (MacMillan) and Jeremy Harmer's The Practice of English language Teaching (Pearson Longman)are good places to start. One or the other (if not both) will almost certainly be on your reading list for the course. If you start reading one now, you will help prepare yourself for the course, and also pinpoint some areas where you may need to do some extra work, But don't think you have to master everything - that's what the course is for.
One of the parts of grammar that seems to cause many problems for beginning teachers is the tense system of English verbs. Rosemary Aitken's Teaching Tenses (ELB) is a very sound guide - and provides tips and materials that will be useful for you in your early days as a teacher.
You are wise to want to make yourself better able to deal with the course, but don't worry about becoming an expert before you start. You do not have to be an expert on English grammar before you start the course - you won't even be one at the end of the course! If you can identify the names of parts of speech (noun, verb, adjective, etc), can identify most of the English verb forms (present simple, past progressive, present perfect, etc) and have some idea of how they are used, then you are well on the way. It is the job of your course providers to bring you up to the reqired level; all they are looking for initially is an understanding of how the language works at a level that might be expected of a person beginning a university undergraduate course.
You can always post specific questions you have here, or in the 'Ask a Teacher' forum. We'll do our best to help.
That would be a problem for most of us.
Originally Posted by M.A.U.
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