How do you know if your on the correct lead? I have been riding for a long time but can never figure it out and my trainer always has to tell me.

The canter stride has 3 beats and the lead is the 1st beat of the stride. In most circumstances the 1st bet of the stride is taken with the front inside leg of the direction you are going. The inside shoulder is ahead of the outside shoulder and leg in rhythm and the way it reaches out. A quick glance at the shoulder to compare how the two are moving will tell you if you are on the correct lead. Over time, you will know simply by the rhythm of your own seat- for example you will feel independence in your two hipbones do at the canter you’ll feel which one being “pulled ahead”.

In the en its best to watch some youtube videos of horses cantering. Just watch the rhythm an that inside leg vs all three others.