Unrack the bar by driving your shoulders up into the bar aggressively. A lot of people find that, especially with very heavy loads, unracking the bar aggressively makes the weight feel less intimidating than gingerly unracking the bar. Start with your hips a bit behind the bar, take a deep breath into your stomach, tense your back, and drive the bar up off the hooks by driving your hips under the bar and pushing the floor away from you.