I'm no dancer but I seriously looked into this. Just singing along, I believe it's...
Listen to the constant bass, that's your beat. Every time your hips swings and stops at the sides, the beat hits. It never hits when your hips is around the center.
1(bass beat), 2, 3(bass beat), 4, 5(bass beat), 6 Do(bass beat) It! (
1st "LA" you have your hips pop to the left while you make your right shoulder directed towards the right.
2nd La should be in the center.
3rd La should have your hips to the right while your left shoulder is now directed towards the left.
4th La should be in the center.
5th La should be like the first pop.
6th La should be the center.
(Silent La) there's no singing, the song stops for a second but your hips should be to the right and your shoulders back to the left.
7th La should be like the first (by now, you should have your motion already of your hips and upper body going opposite directions.)
8th La is Center
9th La is the same as 3rd.
10th should be center.
11th should be the same as 7th.
Now comes the tricky part.
12th La should be center
There's the pause here but there comes the whip where you whip your hips to the left but bring it back to the right before the next few LA's starts. Kinda like, switching positions to the opposite side quickly but make the hip smack or whip to the side and also raise your right arm with fist enclosed. Make sure you punch the sky at the same time your hips whip to the side and bring your arm back down.
13th La should be coming but by this time, you should be back to having your hips sway to the right. (Yes, 13 and 14's LA ends with the hips to the right and the left shoulder directed towards the left.)
14th LA should be center.
15th La should be the same as the 7th
16th La should be center.
17th La should be the same as the 14th.
18th La should be center.
Now ends the la or like Invincible Youth, star the "1! 2! 3! 4! 5! 6! DO IT!" and repeat lol.
Hope that isn't confusing, just watch the video along with it if you got it.