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When you're first learning studio lighting, the learning curve can be a bit much especially if you're relying on the patience of a human being -- no matter who it is: sibling, spouse, child, grandparent, friend, whatever. There's pressure involved as you don't want to bore the person, you may feel bad about having them sit for hours as you make tedious adjustments.
Aside from using a mannequin, do some fine art shots using your lighting. Shoot an apple, an orange, or whatever else. Obviously, the lighting may be different than shooting the portrait of a person, but you'll have plenty of time to work the lights, you can practice different things, and really come out of it with some nice photographs. If you can learn to make an apple look good with studio lighting, you'll be well on your way to making people look good.