The jumping-start is the easiest start besides the sitting-start.
The start is about 70% timing and 30% body tension. So it is doable for every rider, that is able to ride some laps already.
Position your board on the bench, such that it is parallel to the running wire and bend your knees. It can’t be generally said when you should jump off exactly. You have to try to jump so that you get the tension of the cable in midair.
For the very first attempts I would recommend you to ask your operator. He knows when to jump of and can give you a signal once the time has come.
Now, let’s talk about the actual jump off. A lot of riders jump just a tiny bit to the front and have problems compensating the power of the cable once it pulls you.
I would recomment you to jump high and far. You can do a dry run for the jump off. Stand on a stairset with about 2-4 stairs and jump down. You need to jump forward for this and bend your knees at the landing. Do this a few times to get the motion routine.
Then put on your board and jump forward a few times on the dock to get a feeling for the jump with a board. If you are save with this, you can stand on the bench and gather all pieces of the trick together. Wait until your operator gives you the signal to jump and then jump forward. Keep the full body on tension and pull the handle to the hip. If you want to start left foot forward, pull the handle to your left hip. If you want to start right foot forward, pull the handle to your right hip. The board will then turn in the right direction automatically. So, don’t try to jump with one foot forward actively.
At the landing you bend your knees just like at the stairs practice. If your jump off timing was correct you will get the tension of the cable in mid air so you can ride on directly.
If you jump off to early, you might land first and then get the tension. If you jump off to late, the tension will come at the start of your airtime. If you don’t have full body tension, then you will fall over to the front.
You will need some tries to get the right timing first. So better ask your operator to give you some help.