Take a shoulder-width overhand-grip of the bar, and keep your toes pointing straight forward.
The name of the exercise (“stiff leg”) is misleading; you actually need a slight bend at the knees to get the full benefits it offers.
Let the bar travel down the front of your legs, pushing your butt back (imagine you’re trying to push a button behind you). Depth is different for everyone, you’ll feel your hamstrings stretch like a motherf**ker when you reach your limit.
Watch the video demo; notice how my back stays nice and flat when I’m at the bottom of the rep? That’s because I keep my chest up and shoulders pinned back, which prevents my lower back from rouding.
How do we get back up from the bottom? Don’t just think about standing up… think about driving your hips forward, this will force you to fully engage the power in your hamstrings and glutes.