@mmskiboat It takes more to describe, but I'll give it a shot! I'll describe for a left-foot-forward (LFF) skier.
For starters, I pinch closer to my actual knee (left elbow, left knee). My right forearm close to the elbow pinches just below the knee above the calf muscle. The idea being you should be in a tight ball with your back leg up as close to your body as possible. By pinching with your arms, you create a small, compact ball that follows the handle as the boat (gently) pulls you forward.
Before I tell the driver I'm ready, I put the ski on a 45-degree angle to the left with the rope to the right of the ski. This slight lean is much easier to maintain while the boat gets set. Also, it will make it almost impossible for you to roll over to the right.
When I'm driving a newbie who's learning 2-foot starts, I will put the rope off the left corner of the transom and keep it there until I hear a "go boat." I straighten the wheel before accelerating. This mean the boat keeps turning in a slight circle until accelerating. By doing this, the skier is no longer being forced into perfect alignment with the boat... boat -> rope -> handle -> feet -> ski. This gives the skier the opportunity to balance in what becomes a 3-point stance. The skier is actually no longer directly behind the boat and will get pulled back to centerline with their body being "open to the boat." Your feet are no longer in alignment with the directional force the boat is applying and therefore your body has a chance to achieve a little bit of left/right balance through your feet. It is subtle, but I find it helps those who are learning. Eventually as one gets more comfortable this is no longer needed. In a way, it is similar to what I teach people getting up on a wakeboard for the first time.
If the skier is not intentionally leaning to the left, I will watch for them to unintentionally lean left. It is almost always bound to happen as the skier is adjusting their weight to stay in position. I never give the boat gas if I see the ski leaning to the right as that's a recipe for failure 99% of the time, in my opinion. Even just a very slight angle to the left will help the chance of success.
As others have described, when getting pulled up 2-foot, it is important to keep your butt as close to your back ankle as possible. The closer to your ankle, the less water in your shorts. You'll know when you are doing it right when you don't get bogged down by ballooning shorts. ;-) If you wear tight shorts this won't be an issue that you'd notice. I'm not sure how else to describe the sensation, but when done properly, the get up is very effortless.
I have a friend I ski with in Maine. He has had a bad back for decades and gets up 2-feet in. He probably weighs between 200-230 pounds depending on the summer. He asks for a very gentle start. I give him a softer start than I give my wife, who weighs in at approximately half his weight. And he pops up quickly too. I say this just to point out that it is more about finesse than muscle.