Since I'm so obsessed with eyebrows as I mentioned here I decided to share with you my technique:
Step One: Tweeze hair between brows without making them too far apart. Go as far down as you need, if you have stray hairs towards your nose; get those too. This will allow your brows to look nice and neat.
Step Two: Take a small scissor and trim longer hairs in the same angles your natural shape. This will show you which hairs to get rid off.
Step Three: Continue working on the outer part of the brow and get rid of any hairs that would potentially connect your brow to your hair line.
Step Four: Start from the lowest part and eliminate hairs that you are certain need to go. Continue working your way up stepping back every so often to see the bigger picture (only use magnified mirror to see if you missed any baby hairs.
Step Five: If needed tweeze extra hairs that may affect your shape.. try not to get carried away.
Step Six: Once you have your desired shape you can fill in any gaps with a pencil going in the same direction as your hair growth. You don't want to fill in the entire brow merely add a shadow of color where your hairs may be thinner. I like to do this stepped away from the mirror so I see it from a distance.
image: google search