A look of a dull looking onion could speak almost everything about your kitchen skills. If you have been seeing uneven pieces with squashed pieces, or if you are struggling while holding your knife on the board, then you are likely rushing the motion before your muscles remember what you are doing. It does not mean you are going to learn how to cook with quick movements. But instead, you should have to learn what you are going to do when you want the pieces to be unbroken and to stay as you cut. The better you get, the more peaceful you will feel when you do prep work for a dish. You will notice that your ingredients will cook more uniformly and less crushed when you handle your knife skills well.
First, you want to learn to keep control. If you have not done much cutting before, start with an ingredient that gives you clear feedback. Pick up one onion, a carrot, or a cucumber, and cut it in half to rest on your board with one side flat. You hold the knife without squeezing so much that your hand will be stiff. Then with the hand that guides the knife, curl your fingers, pointing the knuckles toward your blade, and you will notice it does not move every time the knife slices. Instead, move it along to get another cut. You do not chop. You cut, then guide the knife into another piece.
Practice for about fifteen minutes. Cut one thing for about five minutes and see if you can get it so that each piece is about the same size, like slicing a cucumber into pieces to cook into a stir fry. Then chop another onion or garlic and see if you are cutting the tip of the blade. Finally, look at what you cut before you move on to other things, and see if anything looks uneven or smashed or thin in some areas or thick in others. You can see that you are better at this if you look at what you cut. If the pieces look different, ask yourself what you did wrong. Did your board shift? Was your knife angled wrong? Did your guiding hand move differently? If you are going to practice well, then look honestly at what you are doing and do it better the next time.
Also, you need to pick the best ingredients to practice with, as some will not work well until you are more comfortable with knife skills. Do not worry if your knife feels a little wobbly. Do not assume that you have no talent. But do pick a different ingredient to practice with before you work with sweet potatoes, a hard squash, or a tomato. Pick up a cucumber, a stalk of celery, an onion, or a peeled carrot. You should find that they offer you better feedback as you learn to cut. Then practice with soft herbs or hard root vegetables. If you find that it is not going well, slow down and cut the motion smaller. Wide swings are likely to make you less accurate. Smaller movements teach the hand where to take the blade.
If you feel you are not improving, do not push for more of the same. It might be your posture, table, or shoulders. Stand close enough that you do not have to stretch to work. Use a towel under your board so it does not move. Relax the knife hand shoulder and free the elbow. And then cut ten pieces, stop, look, and see if you made any corrections. Did you squeeze your handle tighter? Are your fingertips a bit higher up? Do you feel that you can take the knife at a slightly different angle? If you change several things at once, you will have nothing to tell you what to try next. But if you change one thing, you will find your answer. Better still, if possible, cook the pieces you cut, so you see if your carrot pieces look like they are not all cooking at the same speed, the thin bits will soften quicker than the big lumps.
The skill will come with time and patience. You build a steady hand one cut at a time, and on the board, you see where you made errors in that one cut. It means more than good-looking slices. It is how you affect a texture, cook evenly, and how you feel as the meal moves forward. In a week of practice, you may find your hand is moving more smoothly, less slipping on your ingredients, your cuts have a cleaner edge, and it feels like a more natural place to guide the knife.