I am a 2nd year MBBS student. What should I do to appear for the USMLE entrance exam for PG?

The best time to prepare for step 1 is either after or during 2nd year of MBBS. But If you are preparing during second year, be careful that it is not affecting your preparation for professional exams. After thorough preparation you can appear for the exam in the mid of 3rd year. Many students also start preparing during internship and get equally good results. But then you have to wait for an extra year to apply for residency. You need atleast 7–8 months of dedicated time to prepare for step 1. So manage your time accordingly and take the test only when you are fully prepared and confident to appear for the exam. Don’t hurry!