I give them the option. Most want to go
fly versus sightseeing. I generally let them takeoff (they control the
yolk while I control the power and rudders... all depends on your level of comfort). During climbout and enroute to the practice area I generally let them maintain control of the
yolk while I control power and rudders, I may use trim if they start going goofy on the altitude. Once out at the practice area I give them everything and sit back with my seatbelt on tight

. When it's time to come back in to land I generally take over for everything once the approach gets to the point of having to put in flaps. The key is to let them think that they are flying all by themselves (which is why you give them the
yolk) and it actually works out pretty well. You don't realize how much power you have with only your throttle and rudders until you start flight instructing lol
my .02
EDIT: Explain what to do for the takeoff before you give them the
yolk as well as explaining basic terms you may use while letting them fly the plain i.e. increase pitch, reduce pitch, roll wings level, etc.