A canker sore is a little crater on the lips, cheeks, tongue, or most often on the gums. They usually start out as a little red bump. Eventually it will pop and will be a white or yellowish crater like thing with a red border. It burns and stings a lot. It might make consuming food a very hard job. They usually last around 4 to 7 days. If it lasts longer and the following tips don't help, contact a doctor/dentist immediately.

[edit] Steps

Use an over-the-counter medicine such as Oragel specifically for sores and oral pain. Keep it in your mouth. Try your best not to touch the sore with your tongue. You will notice as the seconds tick away that spit has gathered in your mouth; keep the medication in your mouth and try to guide to the affected area. Don't use medicines for teething help and other non-canker sore type issues it wont do anything but end up worsening your pain.
Use an ice cube.
- Make the sore a little wet by running it under water for a moment because otherwise you may experience discomfort from the cold of the ice cube.
- Wrap a napkin or tissue around the ice cube and apply pressure to the sore. You will notice your mouth going numb.
- You will experience quite a bit of pain but most of the time it is just from the cold of the ice cube after every 15 seconds of having the cube on the sore, fight it off and use gaps of 5 seconds then apply for 15 seconds and repeat.
Continue this for a few days -- soon the red bored around your sore will become yellow or white and fall off. When all you see is the sore and no border except your gums or cheek or w/e. Apply Oragel and after 15 minutes ice it again. This will make your mouth numb.
Wait about another day for your mouth to heal.
the first 2 seconds that you put the ice cube on it stings the most.

[edit] Tips

Fight off the pain. You can handle it.
The ice cube will hurt a lot but fight off the pain. As your mouth gets numb try to apply the cube for longer periods for like 20 seconds or so then take a break.
Don't put your tongue on the sore at anytime, because if you do it after numbing the pain will return in a fraction of a second and even worse this time.
If you have sensitive teeth, go easy on the ice cubes. Try to lower the cube so only the top touches the sore away from them pearls of yours.
Get enough sleep. Canker sores can be made worse by stress and lack of sleep.
Wait a few days. Yes, it's painful, but be patient. Most canker sores go away on their own.
Do your best to keep teeth, braces, and sharp foods away from the sore.
Gargle affected area with salty water

[edit] Warnings

Don't swallow the medicine.
Don't eat spicy foods, they will make the pain much worse.
Don't eat salad dressing. It burns very badly.
Avoid high acid foods. They may exacerbate the problem.
It is a horrible feeling to be eating something sweet, and having the sugar stick onto your canker sore, because you have no other option except to prod it out with your tongue and that hurts. Avoid eating foods with sticky sugar like pop tarts.
Avoid temptation to engage in popping the canker sore. Such behavior may lead to infection of the canker sore and subsequently, you will be in more pain and it will take longer to heal.