When it comes to cutting up fresh herbs, you need to know how to properly slice, chiffonade and rock chop. In this video, J. Kenji López-Alt from Serious Eats demonstrates each technique and explains which is best for certain types of herbs.
The slice is best for herbs like chives or spring onions. To do it right, you'll want to hold the blade of the knife just past the handle between your thumb and index finger, and make sure you keep your fingers curled back, your thumb tucked underneath them and your knuckles resting against the blade. Then pull the blade back and forth, using the weight of the blade to slice through the herbs horizontally as you pull back.
For the chiffonade, which is best for herbs with big leaves, you'll need to make some stacks first. Once you have the leaves stacked going from biggest leaf to the smallest, roll it all up into a cigar shape and do the same slicing technique as before.
When it comes to herbs like parsley or coriander, the rock chop is your best move. Gather up the leaves into a loose ball and hold them bunched together with your curled back fingertips. Slice them up, then place your free hand on the top of the knife and rock it back and forth over the herbs until they're finely chopped. To store your freshly cut herbs, you can place them in a container covered with a moist kitchen towel for a few hours, or refrigerate them in a plastic container for up to a day.
Knife Skills: How to Cut Herbs [Serious Eats]