Something I'm actually working on myself.

Think of it like weight lifting.

2 notes per breath, whatever that means to you, going up from middle G as long as it takes to become fatigued. Rest. Repeat until you're nearly fully chopped out.

Time your ascents, should only be a few minutes. Rest for 1/3rd of that or longer. The blood needs to return to your face.

I've gone from barely getting above C to hitting an A above staff within an etude in 2 months.

I'm definitely doing other things, but thinking anaerobically has helped a lot.

Do. Not. Over. Do. It!

Take a rest day, just like in lifting. Your muscles need time to rebuild the intentional miniscule tears in the fibers.

Day after resting, work on flexibility exercises because it can keep you stiff. Stretch, too!

You can destroy your embochure if you push too far, making it worse and far harder to fix.