Often these annoying critics don't realize that they aren't coaching. For example, junior officers can be unwitting critics, because they are determined to insure that their team meets or exceeds every standard. No one understands this better than experienced NCOs, who have seen many lieutenants over the years. They are among the best coaches at steering lieutenants away from this type of behavior, as in "Sir (or Ma'am), let me handle this. I'll take care of it." Over time successful military leaders learn to avoid being a critic and embrace coaching. This doesn't mean that you avoid confronting problems or poor performance, which must be done. Rather, that you use the coaching approach to problem solving with people.
On a more personal level, you can become a serious critic of yourself by finding fault and focusing on the negatives in your life. Society encourages us to make lists of our deficiencies. All the things you don't do well that need to be fixed. From the need to lose weight, to work out more, to complete that college degree, to spend more time with family, to get a better job, to avoid arguments with the boss, to make people like you --- the list goes on and can be very personal. It can also drag you down and be discouraging, if you let it. Instead, start focusing on what you have accomplished, what you do well, and in what aspects you are ahead of your peers (and there is almost always something that you do better than most people). Keep a positive list. Write it down, update and look at it regularly before you work on the fix-it list. If you screw up, ask yourself, "OK, so what did I learn from this?" and then move on. When you do well or achieve a goal, take a moment to commend yourself. This is what good coaches do. Despite all the critics out there, inside you are a winner, and you must be your own best coach.