There's a LOT to consider...It's easy to get someone up in the air and hand the controls over to them, let them fly the plane level at first...It's almost easier if you have a buddy box/wireless trainer setup going to help them, and know when to take over if needed.
One of the biggest things that people have problems with is when the airplane is coming towards/past them, and they have to make the mental adjustment of "right is left, left is right" - I see a LOT of people initially struggle with that. One of the easiest ways around that is to set up an airframe where there's no wing attached, just the receiver, fuselage, battery, etc. that will run without flying. Have them taxi up and down the street/driveway/field, until they feel comfortable with left vs right when going away and coming towards them, before they fly and add up and down into the mix...