You'll need a small beard trimmer with plastic attachment to complete this task. Sure, you could use a comb and scissors, but using a trimmer is quicker and less dangerous. To trim the eyebrows, simply place a guard on the trimmer (start with a longer guard as you can always go shorter). Run the trimmer along the eyebrow from the temple to the center of the face (against the growth pattern). If, on the first pass, you don't think the 'brow is short enough, use the next guard size down and repeat. Quick and painless.
Just make sure the guard is securely placed on the clipper and never use a bare blade to trim the eyebrow as the bare blade will take the hair completely off. Nothing looks more strange than a face with no eyebrows and those suckers take forever to grow back!
If you feel your brows need shaping, this is a task best left to your barber or stylist.