If you're uncomfortable about shaping your eyebrows yourself, go to a salon and get them professionally tinted, plucked or waxed. Then simply follow the line when you tidy them up at home.
When plucking your eyebrows, follow the natural line and pluck between, underneath and above eyebrows if necessary. Think about what suits you and don't worry if both brows aren't symmetrical.
Avoid creating an unnaturally exaggerated arch; the shape you're aiming for is thicker at the inner corner, tapering out over the brow bone.
To add definition to your eyebrows and perfect their shape, apply a little brow pencil or dark powder eyeshadow with a small brush.
When defining your eyebrows, pick a shade that's deeper than your own hair colour, but not so dark that your brows and hair become an unnatural and unflattering contrast.