I disagree that there needs to be a formal briefing, this will just get people more nervous and if the proverbial hits the fan they won't remember it anyway. Like most things in life we're dealing with risk vs cost vs benefit; the risk is vanishingly small, the cost is that they will be more nervous and there's likely to be very little real benefit.
The simple solution is to show them how to undo the straps whilst helping them to strap in, and showing them how to open the door/canopy while shutting it for them - this can all be done without them realising they are being briefed. If you need to influence the evacuation sequence then this would be part of the pax brief during the forced landing process; as would the brace position. The pre-flight brief covers basic EoC, show them where the brake pedals are while getting them to taxi to the hold, if you get them to follow-through (or fly) the take-off you know where the hands and feet are.
The only difference is when they're wearing a parachute; they MUST then be briefed on when it might be used, how they will know to go (without relying on intercom), how to evacuate and deploy, and the basics of how to land.
It's really very simple, keep it that way.
HFD