Do you have any bad habits or fears that you would like to get over. Do you have negative thoughts about failing at school, getting sick, etc. Do you overeat, skip exercising, bite your nails or hair? Put things off that need to get done? Have fears about something, like public speaking. Do you want to lose weight? Stay more fit? Do better in school? If the answer is yes, just keep reading.
THE RUBBER BAND CURE
Get a thick rubber band that fits comfortably over your wrist. It needs to be loose so you are not bothered by it. Snap it hard, but not to the point of bruising or anything.
When you are doing the bad habit you want changed, like skipping exercise, not doing your homework, or have a negative or fearful thought, just pull on the rubber band and snap it on your wrist. It will sting and that is what you want.
Right after you snap it, tell yourself to stop doing what you are doing and give yourself the correct action you want. You need to be very clear and keep it simple. For example, if you feel like eating a bad snack, snap it and tell yourself to stop thinking about it. Give yourself something positive to replace the thought, like eating a healthy sweet apple instead.
If you are over afraid of a spider and see one, snap the band and tell yourself to STOP thinking about it. Tell yourself to just relax and move on. Not studying when you should be? Snap the band and remind yourself how important it is to study. Give yourself something positive right after, like thinking about a fun activity you will do after studying and the good feeling you will have getting a higher grade on your exam.
In the beginning wear the band as often as you need to, but you can reduce the time as you get over your problem. You will eventually not need it. You only need to wear it when you think you will need it. You don't need it while sleeping. You can keep the band in your pocket and just put it on when you need it, so it does not have to be actually on your wrist all the time, which would look odd.
Let me know if this helps you. I read a lot about it and it has helped me. There is a ton of science that backs it up too. It lets you communicate with the very "low level" part of your brain that causes these problems, even though the higher level part knows it is wrong. That low level part just knows to avoid things that hurt, so you need to communicate with it to fix your problems at that level.
Note: If you don't have a rubber band available or feel embarrassed doing it in public, you can also try something else, like giving yourself a slap on the top of your wrist when nobody is looking. Remember to always give yourself a positive command after doing it, since that is a very important part.