Your brows must be suitable for you, if they don't, they should be shaped by a professional.
Your extra-long hairs available on your brows, should be trimmed. To achieve perfect results, ask a brow expert to do this for you, or even your hairdresser can come in handy for this one).
Frequently check brows from the side, use a second mirror to check your profile view.
Match your brow pencil to your brow hair color, not your desired hair color since the difference would be too obvious.
If you lighten your hair color on your head, then you should be comfortable lightening your brows.
Make sure you buy brow mascaras. They are awesome for temporarily lightening or darkening the brow since they have a gel formula which holds them into place. Brow mascara comes in the market with a variety of colors, if you are a redhead, you can buy one that matches your head hair color, to tonally tie everything together.
Don't wax your brows on the day of an important event, since wax eliminates a light layer of skin and makes it impossible for foundation and eye shadow to adhere.