It is a good idea to take courses that are very, very closely related to your thesis or professional paper. Talk to your advisor. If you haven't given a colloquium yet, you should. Testing the waters with an informal departmental colloquium before a formal defense is usually a good idea.
Writing a thesis or professional paper is probably going to be the hardest thing you ever did. Writing well is an art. You may have stunning results, but if you can't communicate these results to your audience the results are useless. Writing well is not just a matter of having a good vocabulary, being grammatically correct, or being a native English speaker. Part of your advisor's job is to make sure you produce a well written document.
Finally fix a date and time and prepare to defend your work. Your advisor will know when you are ready and have a good chance of surviving the defense. You will, of course be subjected to a vicious, subversive attack from the committee and whoever happens to come to your thesis or professional paper presentation. Unless of course, your departmental colloquium convinced everyone to stay away. Bringing food and drink has been known to distract the committee enough for students to make their escape from the department and university with a Master's in CS.