I find the ahh ooo helps me relax. Another way of doing this is sighing down the trumpet with the mouthpiece totally inside the mouth then trying the sighing to play a G in the staff.. This is a technique from Paul Mayes that I also find useful. I also hum the drones from C to C that helps relax also. Unfortunatley I have not found a way to get above the D in the staff using these techniques and I have to really blow hard to get the G and most of the time I don’t.