Try not to fall for head fakes, shimmys, or other fakes where the thrower doesn’t move their feet.
Stay on your toes, and keep your weight above your feet; if you over-balance, you won’t be able to react quickly
Small steps are faster than big lunges
Move around where possible; a moving mark is harder to break.
Marks often use their arms as a crutch when they aren't actually covering options as well as they could be, and they lean their body instead of moving their feet. Move - Your - Feet!
When done properly, this drill is quite exhausting. It will show participants that marking should not be considered a rest if they are to do it properly.