First only fill in where you have holes or thin hair, you do not need to go over the whole brow, only apply color where needed.
Next, after you apply color go over it with an eyebrow brush or mascara spoolie to soften and blend the color
All lines offer some kind of brow color. You can get an eyebrow pencil or powder. If you have blonde or red hair you need to use a blonde pencil. If you are a brunette use a brown one. If you have very dark or black hair either use a dark brown color or black powder--I do not suggest black pencil on eyebrows.
An awesome brow color product that is super cheap is NYC Browser Brush-on Brow Powder with Grooming Wax and Tweezers. While I don't think the tweezers are worth even trying to use, the brow powder and wax are great!