Go all the way down until your thighs are compressed against your calves.
Go down in a controlled manner, without falling quickly into the bottom position.
Feet stay flat on the ground, with your weight evenly distributed on them.
Knees stay out: do not let them cave in when you go down, but pull them out with your glutes (butt muscles). They should be aligned with your toes when going forward.
Ideal feet width and angle depends on your body mechanics - play with different positions to see what works best.