Lie on the bed with one leg fixed and the other leg lifted up. It's best to stick to it for a minute and a half, and swap left and right. You can also lie on the bed like a real man, with your legs raised at 45 degrees (neither too high nor too low) or stick to it for 40-60 seconds, take a break, do it by yourself several times, or do aerial cycling (greatly), squat, squat, etc.