Before you can get good lead departures and waaay before you even think about flying changes, you need to know what lead you are in on the very first stride the horse takes. Once you get good at this, you can feel what lead a horse is going to take before they take it. Until you can tell on the very first stride, you cannot get a horse really solid on lead departures. The way you get a horse solid on lope departures is to interrupt the horse mid-stride any time it attempts to take the wrong lead. When you get it in the correct position to take the correct lead and it does take the correct lead, then you let it continue on without stopping it. This is how you get a horse solid on leads. But, the same is true if you let them continue on in the wrong lead while you are figuring out what lead your on. By the time a horse has gone 2 or 3 strides in the wrong lead, he thinks he has done it right.
For now, you need to concentrate totally on learning to 'feel' what lead your in until you can tell on that first stride.
There are several ways to tell what lead your in. Look down at your horse's shoulders. The lead he is in will make that shoulder look like it is farther forward than the other one.
Your foot will be farther forward on whatever lead you are in. If your horse is on the left lead, no matter what you do, your left foot will stay slightly more forward than your right foot.
The horse's leading front foot will be the last to strike the ground in the 1-2-3 beats of the lope. Concentrate on what foot is striking the ground and pretty soon you will know exactly what foot is getting ready to hit the ground.
In the beginning, you can lean over and double-check by actually watching that leading front foot hit the ground. You should not have to do this for very long. It is sure not a good idea to depend on this because the horse is going to travel too many strides in the wrong lead if that is the one the horse took.