Using e/s to fill in your brows should give a more natural look. Lots of brands sell e/b powders too, including NYX and Ardell. And they usually include a little brush with them. If you don't have one, you can get a stiff angled brush at places like Target, Walmart, Ulta and even the craft store. Something like this:
Get some powder on your brush and then make small strokes in your brows in the same direction as the hairs. Use a light touch to begin with. If you want to add more color to any bare spots you can add a drop of Visine to the powder before loading your brush, then apply wet. Let dry if needed and then brush through your brows with a clean e/b brush. Let me know how this works for you!