According to my Motorola TTL manual:
1. J low & K high, clock produces reset state.
2. J high & K low, clock produces set state.
3. Both J & K high, state toggles with clock.
4. Both J & K low, clock produces no change.
Frankly, JK's make me itch. I always use D flip-flops. There's nothing inherently wrong with JK's, but they are always uncomfortable to use (for me, at least).