Make sure you are well rested and have sorted out as many practical/life issues (that are sortable) as possible in advance. For example, make sure that your living arrangements and finances are in place, and any other practical things that could cause stress if dealing with them alongside your course.
I wouldn't worry too much about doing loads of reading, but a skills self audit might be good, as chickpea suggested. Find out what training and courses might be available to you through the MPhil (i.e. don't spend time and money on honing a skill that is covered in week 2 of the course).