Imo basics of controls and economy ..
Stuff like scrolling, selecting stuff, concept of metal extractor and energy/metal storage.
It cold be followed by advanced tutorial with overdrive and priorities.
If you find those tutorials hard to make, it might be easier to make tutorials as videos and only make practice missions focused on those aspects. Like mission where you must build economy or you are overrun by programmed waves of enemies or something.
Regarding map - perhaps some smaller nice looking map .. flatter so there is no issue placing structures..
Perhaps some tnm map? (Go to maps search tnm)