All of the above. Exaggerated head movements are important; get into the habit of moving your head to point to whatever you're looking at, and that includes your mirrors. Even if you're diligent with eye movements you need to move the head so the examiner can see. The tape strip on the helmet is a great idea to give them a reference mark,. especially if your helmet has no distinguishing lines or features they can key off.
When slowing, as when approaching an intersection, apply enough brake to light the brake light as you're going down through the gears, even if it's not enough to actually apply the brakes; the light is important when you're slowing.
Study the checklist. Make note of stuff like not moving your feet at a stop, stopping at the right position (e.g. before the white line or before the line pedestrians would cross etc). Make sure you do traffic checks each stop and each start. Even at a stop, keep moving your head doing "traffic checks." Check your mirrors and signal before initiating a lane change.
Don't do as I did and lose the examiner on the highway portion

Don't speed (excessively, anyway; go with the flow of traffic...)
It can be stressing because it's an examination and a pretty big milestone but the basic fact is, if you're ready for the test you won't have to remember much from the checklist; most everything on there should be natural for you by the time you're ready to get your M endorsement. It'll just be you going out for a ride, just with with some guy chatting in your ear to turn left, turn right, enter the highway, change lanes, roadside stop etc...) Look at the list and see if you've developed any "bad habits" since getting your M2 -- such as not staying in the correct tire track, not checking traffic after stopping and before moving off, speeding, changing gears in an intersection, riding with one hand on the bars etc -- and work on cleaning up that stuff, if only for the test