How to initiate Preset and Clear in a JK flip flop?
Your lack of reference to the type of JK FF prevents a specific answer, however in general you want the J &amp; K inputs connected to a logic 1. The preset and clear inputs will be either active-low or active-high. 

In either case, assuming you wish to clear the FF, you want to drive the clear input active during initialization, and to inactive later. The preset input should remain inactive always.  

The 74HC73, for example, has only a reset input, and it's active low. So you want to generate a pulse that lasts for some small amount of time after the power has reached the proper level, and that pulse should be low, followed by a high level forever. A 4027 has both inputs, and they are active-high, so you would tie the preset input low and pulse the reset input high at power-on. 

By the way, 555's and RC circuits are not reliable ways to reset logic. I advise using a proper reset chip that has a voltage reference built in and a time delay on the output pulse.