If you understand what the clutch is used for, then you will know when is it appropriate to brake first or clutch-in first. They should teach a little bit of these mechanical parts stuff in driving schools. In fact, my opinion is that a lot of driving schools and so-called 'driving instructors' out there are incompetent.

I would not advice you to get yourself used to clutch-in-then-brake all the time, as you would be removing the engine braking assistance in case of an emergency. Meaning, it would take you longer to stop and higher risk of your tires locking which means even longer to stop.

Despite my long reply, the correct way is to brake first, then clutch-in to avoid engine stalling when the rpm falls too low, usually just above your idling RPM (800-1000 RPM). When you're just starting out, it's always okay to clutch-in earlier as you're not used to driving a manual or the car.

Heel-and-toe and all that, you can save it for when you've finished your driving lesson and out of your Probationary period. Stick to the basics.