How do I figure out what eyebrow shape is best for me, and then how do I pluck my way to that shape?

Look at your natural arch and follow that. Your eyebrow should start at the base of your nose, then arch over the middle of your eye and end at the corner of your lid. The easiest way to see this is by taking a pencil and holding it straight up against your nose and the inside part of your eye. This will give you your starting point. Then moving only the top of the pencil, move it to the center of your eye. This is where your arch should be. Moving the top again to the outside corner of your eye, this is where your brow should end. Pluck the little strays around your natural shape. If you're still tweezer shy, go to a professional and have them shaped professionally the first time. From there it is really easy to maintain the regrowth by tweezing or waxing. Hope that helps!