First, consider the starting point of your eyebrow. From your nostril, think of a line headed straight up to the brow. At this point is where the perfectly arched eyebrow begins. Mark it with your brush.

Next, imagine a second line extending from the outside of your nose, diagonally up through the outer edge of your pupil. The point where this line hits the brow bone is your eyebrow arch. 

Lastly, the eyebrow ends from a third line that starts from the outside of your nose and slants upward through the outside corner of the eye. There, you'll mark the ending point of your eyebrow.

For some eyebrows, once you've created the correct brow line, you may notice spots of the brow that appear too sparse. You will need to fill in these areas with color. When the eyebrow is sparse closer to the nose, you will usually select a lighter shade to fill it in as a color too dark near the bridge of the nose can create a scowling sort of effect. Save the darker shade for filling in the outer portion of the brow. 

For some, there may be a bit of asymmetry. There are many products available to help you fix these imperfections. Ideally, you would fix these imperfections with a brow shadow. But a regular eyeshadow in an appropriate shade will work just fine. 

In the case of the unruly eyebrow, dab a touch of eyebrow wax to the starting point of the brow and comb through. There may be rare moments that require an eyebrow pencil to come to the rescue and fill in any gaps across the brow. The idea behind the eyebrow pencil is that its tip is so tiny, it is difficult to make a real mistake. Even so, whenever you're using an eyebrow pencil you should always use short, feathery strokes. Once the brow is arched, you can top it off with highlights just beneath the brow. Again, brow shadows or appropriately hued eyeshadows will do as well. 

Another thing to note about eyebrows is that, while they may be sisters to a set, they are certainly not identical twins. There will be slight discrepancies in symmetry, and that's just fine. No two brows are alike.