Look at the tip spin thread. This seems to have been asked alot lately.

Do a knife edge up high, cut the throttle, keep feeding rudder to hold the knife edge, when it stalls and starts to fall give it full down and aileron the same way at same time. Should go right into it. Thats how mine does it.

Then as it falls reverse the rudder only to go into a inverted flat spin, then move the rudder back to enter the tip spin again...