https://www.youtube.com/watch?v=blYxIGHPYTQ In fact the angle of the thigh should reflect your skill level.--higher either means you are more functional user you fight or do applications. Deeper is more for training-better flexibility should come from drills as form practice a combination functional and training. Flexibility by drilling flexibility is more show and allows ability to get into position but require strength and functionality for better usable.

Keep your heels on the ground unless you do a cat stance /false step stance.

Rear foot is always toes forward flat foot. You can be completely straight if you step to the side of your front foot. This turns in the thigh supporting your stance I think.-Ernie Moore Jr.

When you step forward step-out some so the heels are not on the same line in that direction.

Use socks wit grip on bottom or no socks or a mat with more friction--slipping stresses your knees.

https://www.youtube.com/watch?v=_hlxYxUhwjY&feature=youtu.be