Get a good and comprehensive book. International Law by Tandon & Kapoor is easy and detailed. You can cover most parts from it. Get the Study Plan from other threads and start reading according to the mentioned topics. It is all self study and understanding. Some memorizing and interesting concepts. See the past papers. Look into the current international issues and Int. Law's take on them, eg. Ukraine, Syria...research what Int Law says about them. Don't forget doing the paper papers of 5 years at least, solve them completely.

No teacher can do that! Only you. And its definitely not easy but not impossible either. So gear up and start preparing.