Upright flat spins are beautiful, easy to execute and easy to get out of. For a less experienced pilot, they provide a moment of relief where everything just slows down and for a experienced pilot, they are a great way to transition from high speed flight into slower momentum.
The keys to an upright flat spin is to work the throttle and ailerons together as you enter and hold the spin. Without enough throttle most planes will tend to drop the nose and fly out. I've found that if I gradually work the throttle a bit under half I can keep the tail down and the plane rotates beautifully. If you open the rudder as you descend the spin will widen out and you can gradually circle your plane down.
Give these tips a try!