What is totally essential is to work out (somehow) on the ground exactly what one should be doing in the air.
Damn straight. What you should be doig in the air is practicing the procedures you have already learnt on the ground.
Trying to teah someone how to do anything in the air without a proper briefing before hand on the ground is a total waste of time and a total waste of money for the student subjected to this terrible teaching.
When doing an IMC course I'd often spend a whole day or two (when the weather was too bad to fly, a regular occurance in the UK) going through the whole course one step at a time.
Firstly talking about the differences between VFR and IMC flying, the risks, advantages and the gotcha's.
Once they had a few hours in the air and were starting to learn the basic flying techniques, then they would get the full day or two on procedures and using radio nav aids.
You don't want to overload anyone with information, it needs to be introduced when they are capable of understanding it and one of the biggest problem any FI faces is that of the student rushing ahead on their own outside of the syllabus and confusing themselves.
Of course you need to prepare well, but often people try and rush to the end. I've lost count of the number of times I've been asked to explain the intricacies of an ILS by someone who hasn't even mastered straight and level flight. Of course you explain the very basics, but to go into the depth you would with an IMC student would be a waste of your and their time.