Position body under bar, and place bar on upper back (trapezius). Stand with knees slightly bent and feet approximately shoulder width apart. Keep toes pointed forward or slightly out. Stand in good body alignment (abs tight, chest up, back straight). In a controlled motion, lower body by bending knees and hips, pushing glutes back. Keep a slight arch in the back. Keep knees in line with toes; avoid turning knees in or out. Keeping feet flat on the floor, continue lowering body as far as possible without compromising form (back arched, abs tight, chest up). Stop lowering before pelvis begins to curl under or back rounds out. While maintaining controlled motion, return to starting position (avoid locking out knees). Do not allow muscles to relax before next repetition.
Here are a few suggested alternative exercises:Ball Leg LungeBall LungeBall Wall SquatBand LungeBand Lying Leg ExtensionBand SquatBand Standing Leg ExtensionBarbell Bulgarian Split SquatBarbell Lateral LungeDead LiftDumbbell Dead LiftDumbbell Hack SquatDumbbell Lateral LungeDumbbell LungeDumbbell Lunge CrossoverDumbbell Lunge WalkingDumbbell SquatDumbbell Sumo SquatFront SquatHack Front SquatHack SquatLeg Press - MachineLunge - BarbellLunge - Smith MachineLunge BackwardLunge CrossoverLunge DiagonalLunge Forward