If you are a jumper you need to focus on other things.
Good SLJs are not an indicator of TJ success/improvement, the nature of the jumping events differs vastly from the SLJ, they are a good indicator of explosive power and FT-fibers presence but that's it, you should be working on much more tailored and specific plyometric and strength work for your events.
Anyways training to improve SLJ is eazy since its mechanics are not as a complex as the triple or long jump.
Generally speaking aim to improve max strength in the Squat, Dead Lift and Barbell Hip Thrust (maybe add an auxiliary for calves, you maybe have to do an introductory phase with lighter weights before moving into MaxS depending on your lifting experience), introduce some lower intensity plyos this phase (dont do MaxS for more then 6 weeks), gradually increase the intensity and volume of the plyo work and start replacing the barbell exercise with Olympic Lifts and more specific variations of strenght work, eventually stop doing everything else and start working on just your SLJ and test it by the end of this phase (make sure you are rested and fresh).
A simplistic overview (take an de-load/active rest every 4th week, you can also do one SLJ test here at the last day of the week).
8 weeks(Max. Strength Phase) -> 8 (Power+Oly.Lifts) -> 2w(just SLJ work, peaking and final testing)
or a shorter version if you have less time
4 weeks(Max. Strength Phase) -> 4 (Power+Oly.Lifts) -> 2w(just SLJ work, peaking and final testing)