You're Not Sharpening Your Knives
People need to know that you need to sharpen your knives in order to be a good cook. This is just something that people don't want to do for whatever reason. A sharp knife will make your cooking process much SAFER (believe it or not, sharp knives are statistically safer than dull knives) and more enjoyable. You'll start to take more pride in your cooking if your knives are sharp.
You're Not Letting Meat Rest
Some people pull beef (and other "steaklike" proteins) off of the pan and they immediately slice into it while the outside is still sizzling. This is a super "no-no" in the cooking world. That big juicy cut that you were so excited to eat is going to be strangely cooked, dry, and boring by the time it hits the table. Cutting meats too early will make the juices and fats run out of the finished product. Make sure you at least rest your meats for one or two minutes before you slice into them.