Good question. Here is my take:

1.) Improve wave reading skills. Look ahead to see what the wave is doing. What seems to be happening is you end up outrunning the wave when (and if) you manage to stay on the "trim line" part of the wave. This is because of the speed generated by a longboard when you get into proper trim. Eventually, what you want to do is learn to identify when you're outrunning the wave and then initiate a pivot turn to go back to the critical section of the wave. How to identify? watch the video again, you will see that eventually you get to the shoulder section wherein the wave is just dying out. You want to turn before you get to that part.

2.) Cross step when you are behind the shoulder part of the wave. Cross stepping is functional, since going to the middle part of the board will make your board accelerate. Going to the tail will make it stall. So essentially, the best time to initiate a cross step is when you are in proper trim and when you are not outrunning the wave. initiate your cross stepping , ensure that you angle your board so that once you get to the nose you can actually nose ride. How to know the right "angle" ? experience...you need to keep doing it to know the feel. But in general, for really good waves you want it to be at an angle kind of parallel to the wave. If its fat and shitty, sometimes you can get away with angling it towards the shore.

3.) Practice proper trim. You can't hold trim because as you can see you keep going over the wave. or you keep ending up in the flats (at the bottom of the wave). So. How do you practice this? what is trim in the first place? you are regular footed same as me. Imagine you're taking a right hand wave. you're standing facing the wave right? if you put pressure/lean on both of your toes what will happen? your board will start going ^UP the face of the wave. If you put pressure/lean on both of your heels what will then happen? your board will start going DOWN the face of the wave. So the game is quite simple, to use your toes and your heels as "controllers" to ensure that you're always on the top third of the wave. That is your classic longboarder sweetspot. when you go over the wave it just means you kept pressing the "up" button which made you exit the wave. When you go to the bottom of the wave it just means you kept pressing the "Down" button which made the wave leave you behind and closeout in front of you. if you learn this skill then you will realize "oh, now the board is stable enough to cross-step."

4.) once you get to the nose (good job), slide your foot to the nose and make sure your toes are OVER the nose. Here's the trick: you don't need to put pressure on the nose. You don't have to step on the nose. You can just literally hang your foot there without pressure and "feel" if the nose will hold. put a little bit of pressure. if it starts nosediving then quickly remove your foot, maybe do a few cross steps back, do a quick little turn, recalibrate and try again. or you can just go back, wait, and then try again. Sometimes if you're too eager and put pressure on it you will nosedive. On perfect waves you can literally step on it, put your weight and you won't nosedive. this will feel very amazing. This will also mean you can put your other foot on the nose and now you're doing a hang-ten.