Here are a few tips for communicating with your driver at higher speeds, to ensure the instructions you give are helpful and productive.
Make sure you take them through each manoeuvre step-by-step before you get them to do it for the first time. Preferably do this while you are parked so they can concentrate on what you are saying. Get them to repeat the steps back to you so you're sure they've understood.
Tell your learner what to do nice and early. Let your learner know when they'll need to take an exit or change lanes well before they need to do it.
Once you're learner is reasonably comfortable driving at higher speeds, teach them “commentary driving”.
Get them to identify potential hazards out loud. This is a skill that experienced drivers usually do without seeming to think, but your learner will need to practise this skill at first. Mental practice like this is very important in developing your learner's judgement and awareness.
Sometimes the best way of teaching is to stay silent. Use the WASP technique when the learner makes a mistake: