Honestly, I used to get so frustrated when the glass would wobble. Ngl, practicing with cooler glass helped me get the feel, and now it's like riding a bike.
I used natural gas for years and my pieces would often crack from uneven heating. After trying propane, the flame is much hotter and more stable. My color pulls are cleaner and I waste less material. It was a simple change that made a big difference in my work.
Honestly, tweaking the blowpipe speed did the trick.
Everyone in my class was taught to fuse handles when the glass is at its hottest point. I learned through practice that a cooler, dull red heat makes for a stronger bond. Letting the main body cool a bit before joining reduces stress and avoids cracks. My pieces now hold up without any joint issues after this change.
Fast cooling makes glass brittle and more likely to crack.