I actually draw my eyebrows on, for cosplay, but -- when I had eyebrows, they were slightly thinned out and trimmed down with powder always being my lifesaver.
I know a couple people who use eyebrow wax to cover them up and draw them on from scratch. But if you're not comfortable with that, taking some stick concealer to help lighten them helps! Afterwards, you can draw on top of them with a blonde (or any colour that your wig is). This helps in controlling the shape of your eyebrow (arch, length, thickness, etc.), since every character doesn't have the same brow. Remember that the younger the character, the thicker your eyebrows should be! It helps create a more youthful look. Afterwards, seal it with a powder slightly darker (eyebrows are normally a shade or two darker than hair) or the same shade. This makes it look more natural and helps prevent them from smearing or wearing off.