Although you requested the method of getting into a flat spin, I added a few steps, describing how to get out of it.
Step 1: Make sure your fuselage tank is filled to the brim.
Step 2: When in flight make sure to open your canopy before you start the maneuver.
Step 3: Pitch up to approx. 30 degrees nose high and hold it there.
Step 4: When going below 100 MPH step in the rudder pedal of your choice and roll in the opposite direction slightly.
Step 5: When the spin is stabilised, unbuckle your harness, stand up and make sure you have a firm grip.
Step 6: Carefully climb on the root of the wing.
Step 7: Jump.
And voila you entered a flat spin AND got out of it.
