Eyebrows are tricky as they are rarely 100% hair. You can usually see flesh bleeding through. The two main things are blending the colors and the shape of the brow.
For eyebrows I use a couple techniques as appropriate.
A dark base, a lighter layer or two touched up with an inking of the dark base again and maybe a light dry brushing with the light layer. The last thing I do is to take some darker than base-color and draw a thin line at the bottom of the brow to help define it.
I often like to lightly -- lightly -- dry brush the eyebrows with flesh to soften them. This is done with an emphasis around the edges of the brows as a blending tool.
An advanced technique I like to do is to paint a few light dark-base-color strokes in an up and out diagonal direction -- going with the grain of the brows. I sometimes have to follow this up with a light dry brushing or painting a lighter than base color strokes right next to them. The trick is to not look like I've painted on the brows.
I sometimes curb the eyebrows back with a few flesh strokes going in the same diagonal direction but working from the outside of the brow. The idea is to give a shape to the brow.
Also, a nice petering out to the side is usually what I like in brows.
I hope this helps. I've thrown in pictures for reference. I'm more of a Babe Ruth type of painter. I can't think too much about what I do when I do it.