Knowledge - YES
Experience - Maybe (lots of experience doing it badly - no use. Lots of experience doing it well - fairly rare unless closely supervised most of the time.
Communication - Most Def'.
The hardest thing is to be able to fly and talk about what you are doing to the extent that the stude can learn from your example / words.
In the PPL world I have flown with some very good guys and some very good pilots but poor instructors.
Military wise - same again. However due to the standards required the poor instructors are much fewer and far between.
My two penneth - get some experience and the gain more instructing - not only will you Learn from your student but also when you realise that you actually don't fly as accurately as you think - 'Instructor - see bloggs the reference stays stationary as we fly straight and level - Bloggs, urrrrrm but sir its moving left - instructor, Bugger!'