To Determine Eyebrow Shape...
1. Take an eyeliner pencil and place it vertically against your nose. It should run from the side of the nose, mid-mouth, and by the tear duct of the eye. This is where your eyebrow should start; any hair that is visible beyond the pencil should be tweezed.
2. Next place the pencil diagonally where it should hit the middle of the mouth, nostril, and outside the iris of the eye. This is wear your arch is. Tweeze a gradually line from the arch to the start of the eyebrow. Remember, GRADUAL, nothing harsh.
3. To determine the end of the eyebrow, align the pencil diagonally across the opposite corner of your mouth, nostril, and outside corner of the eye. Any hair that goes past this point should be tweezed.
4. Place your pencil horizontal from the start of the eyebrow to the end of the eyebrow. The pencil should create a perfect straight line.
Other tips for a better tweezing session include:
>> Select tweezers that are slant-edged and have a rough textured point. Replace your tweezers every year or so.
>> Ideally only tweeze your eyebrows after a warm shower/bath when your pores are open... it'll hurt less and you'll be able to extract the whole hair shaft, including the root, and not just "break" the hair off at the skin line. If you haven't showered/bathed, then steam your face w/ a warm, moist washcloth for at least five minutes prior to tweezing.
>> Run a lil' dribble of antiseptic like rubbing alcohol over your tweezers before and after you tweeze.
>> Only tweeze hairs from the underside of the brow and between your brows... don't attack ANYthing at the top of your brows!. If you have especially bushy or, perhaps even worse, one or two especially looooooong eyebrow hairs, use manicure scissors to cut them to length. Use a 10x magnification mirror in really good light to see even the smallest stray hairs. :-)
>> If you've had an "aggressive" tweezing session, rub an ice cube over the tweezed areas to reduce swelling and redness.
>> NEVER apply cosmetics w/in four hours of tweezing and NEVER tweeze your eyebrows w/in 8 hours of a special occasion.
There are eyebrow stencils you can purchase (see link, below) and if you're at a loss as to what shape is best for your face and/or you've hacked at 'em for so long you just don't know what your normal shape/arch is any more, it might be a good thing to get a stencil and "see" what the final result will be BEFORE continuing a process that's not been very successful, ya' know?
Hope this helps,
TX Griff