The key is to use a very sharp knife of a good size such as a chef's knife. Also make sure your herbs are dry before you start chopping as otherwise they will bruise.
Gather the herbs together and hold them with your left hand. Keeping the tip of the knife on the board, slide the knife forward in a rocking motion, cutting with the herbs with the last inch or two of the blade. Keeping your nails and thumb back, use your knuckles as a guide for the knife as you slide the herbs under the blade.