To prevent a zit from getting bigger you have to take special care of your skin until it goes away. Even if you normally are very conscientious about your skin care, you need to put extra effort in during this time.
Keep your skin extremely clean until the zit subsides. Any extra dirt, oil, or contaminants that are allowed to build up on your skin will make the zit worse.
Treat the zit with benzoyl peroxide. There are a number of over-the-counter creams that contain benzoyl peroxide and can help to clear the zit faster. The sooner you get started using one, the sooner the zit will be gone.
Pop it only if it has come to a head. Unless you can see that the zit has a pustule head on it, popping it will only irritate it, which will cause it to swell and last longer. If you decide to pop it, do so with sterile, clean hands and wash and cleanse your face afterward to prevent spreading the infection to other pores.
Take a break from exfoliating your skin while the zit is visible. The pressure and grinding from exfoliation can aggravate a forming zit, causing it to become more apparent. Once it's gone you can resume your normal exfoliation regimen.
Refrain from wearing makeup that could continue to clog the pour. Warm water and soap are the only things you should be putting on your face.
Leave it alone unless you're cleaning or washing your face. Don't pick or poke at it during the day, or allow yourself to constantly touch it. This will only cause more problems and put more dirt and germs on your face when you need to be keeping it as clean as possible.