Like the squat, the Romanian deadlift isn't designed to only target your glutes, but to strengthen your lower body and core, focusing on your posterior chain -- specifically, your hamstrings, glutes, and, to a lesser extent, your back. Also like the squat, you want to load up the weight as much as you comfortably can without compromising form or risking injury. This is because the goal is to build strength and muscle, and the most effective way to do that is to add weight.
Stand with your feet roughly hip-distance apart, your knees slightly bent, holding a weighted barbell in your hands at your thighs. Tighten your core and roll your shoulders back. Keeping your upper body completely straight, start the deadlift by pressing your hips back as you tilt your torso forward toward the ground. As your torso tilts forward, allow the barbell to "skim" the front of your legs. When you feel a stretch along the back of your legs, stop, then tighten your hamstrings and glutes and use them to pull your body back to standing.