To julienne zucchini, for example, cut off the ends, slice lengthwise and remove the seeds. Then, cut the slices in half.
Place your knife in one hand and use the index or middle finger of your other hand to hold the zucchini in place and to determine the thickness of the slices.
Move your fingers back along the zucchini to make the next cut, while holding the flat side of the knife against your knuckles.
During this process, be sure not to raise too handle of the knife too high. Ideally, the tip of the knife should remain firm on the cutting board.
A thin julienne cut is considered to be less than 1/10 inch, while a thick cut is slightly wider.
To julienne carrots, cut off both ends, then peel and cut in half lengthwise. Cut into thin slices and repeat.