Sorry I haven't answered this topic before, Claudia. The little sign alongside the message wasn't 'lit' so I thought I had already commented on it, until saw '0' replies aganist it!
Learning to feel the correect lead often takes quite a while. OBviously the better you can feel the hind legs coming under or striking off the ground in walk and sitting trot, will increase your ability to be able to feel the correct lead. There is no hard and fast way to tell you how to do this. I remember that years ago, I had a hard time feeling the correct lead. One day, I just knew that my horse had struck off wrong. By this time, I had a fairly advanced dressage schoolmaster, and it was on him that I first felt it. Now I could tell immeditiately if the hrose was about to even strike off wrong, and stop it before it happened! Be patient, and work on the feel in the other gaits first. My next video will concentrate in the first half, on learning 'feel'too.
With a horse that strikes off wrong, the best way is to let it run a little bit into canter whilst rising to the trot on the wrong diagonal. This throws the horse onto the correct lead, once he goes into canter. Do this for a while until he gets the idea of at least striking off on the correct leg, then go back to improving the quality of the trnsitions!