This is a very common problem and you're not the only one who has trouble with it. Cuban motion is more easily understood if you explain to your students that it is the same motion the is created when we walk up stairs. That being said, I teach my students to bring their feet together and slowly change body weight from side to side ie:all weight on the right,now all the weight on the left and repeat,take your time,now begin to lift the knee as high as you can without your toe leaving the floor.First we pretend to be in water, then salt water,then sand, then mud, you get the idea, you have to consciously use resistance with every move in order to get the proper look and feel of cuban motion. I find that once my students have this understanding they progress much more rapidly in this tricky motion. I hope this helps. Tom Ramon, Greenville,Texas