You do not need to dice like a line cook. You need a sharp knife and one reliable grip.
Most home cooks are working with a dull knife and a nervous grip, which is exactly backwards. A sharp knife is a safe knife, because it goes where you point it instead of skidding. Learn to hone before each session and to sharpen a few times a year, and half your knife problems disappear.
The grip matters more than speed. Pinch the blade just ahead of the handle, curl the fingers of your other hand into a claw, and let your knuckles guide the blade. It feels awkward for a day and natural forever after.
Practice on something forgiving and cheap -- an onion, a few carrots -- for five minutes a few times a week. You are not training for a competition. You are building the kind of quiet competence that makes cooking feel calm instead of frantic.
