Once you have mastered a clean and controlled flying change, you can begin training the tempi changes (series changes) if you feel ready for it. Tempi changes are combination changes where you make a flying change every X number of canter strides. Tempi changes happen either every 4 strides, 3 strides, 2 strides or every stride. 

Make sure your horse is in good balance between the flying changes and make sure you can half halt after every change. 

If your horse gets excited and rushes off, increase the number of strides between the flying changes so your horse does not anticipate. For example, make 8 strides of canter between the changes. Sometimes counting out loud can help you with the timing of the combination changes.