So, your second step is to search for a trajectory which will arrive at Jool on that date. Try to minimize your ejection delta-V for the outbound leg to Jool. A third thing to keep in mind is the listed insertion delta-v when you arrive at Jool. Last is whether or not your intermediate target has enough gravity to actually make the assist feasible.
get to Jool. Once you've found that window, mark down the date of departure. At the same time, make note of the required ejection delta-v (starting from an orbit of a given altitude; say 500 km). That's the date on which you will need to arrive at Jool in order to make the assist.
Bastante bien, en comparacion a los apuntes de la copisteria