Grab a bar with both hands shoulder width apart, keep your shoulders engaged, jump up and lock out elbows in 90-degree bend; this is the starting position.
Pull yourself up smoothly initiating the movement using back muscles and finish the motion bending the arms; your chin should be clear above the bar.
Pause and slowly reverse the movement back to starting position.
This progression can be useful if you don't have the strength to pull yourself up from the bottom position yet.
Form tips
Do not stretch your neck up to barely clear the bar: focus on quality range of motion by pulling your elbows back and shoulder back to get your whole body higher.