The first week is the hardest, but a buddy can help get you through it.
Spend time in places where smoking is now allowed to reduce temptation.
If you have friends who smoke, ask them not to smoke around you.
Try to avoid situations you usually associate with smoking, or find something to replace smoking in those situations.
Try using toothpicks, cinnamon sticks, sugarless gum, sugar-free lollipops, celery, straws or stir sticks to distract yourself from not having a cigarette in your mouth.
When an urge hits, remember that the urge will only last about 5 minutes. Do something that will distract you for those 5 minutes.
If you use nicotine gum to help you quit, remember not to chew it like normal gum. Instead, hold it against your gums (see package for more instructions).
When a craving hits, don't allow yourself to think that "one won't hurt." The longer you keep having just one, the longer it will take to overcome the addiction.
If you slip up, try again. It takes most smokers multiple tries to quit successfully. Just try to learn from your slip up (where? when? why?), so you can include it in your next plan to quit.
Gaining a little weight is normal. But it is a lot less than people think and can be eliminated once your cravings go away. So first focus on quitting smoking and then losing any weight you gain will be easy.