Fortunately, pop was never my problem. I was raised in the 60s/70s when it wasn't that common and I viewed it as a treat, not a staple. So I never got hooked on it.
But it's like anything else: You just have to avoid putting yourself in its path, you need to make sure you have a substitute, and you need to MAKE YOURSELF say NO enough times that NOT drinking it becomes the new habit. Every time you give in you reinforce the OLD habit.
If you make sure you have none in the house, period, that's the first step. Can you do that? If others in your house want it, put your foot down. No one you love should be drinking anything with ZERO nutritional benefit that contributes to multiple horrible health problems, period. No excuses. Get it OUT of the house for good.
Then you just have to stop yourself from getting it out of machines, at restaurants, and at the gas station. I didn't have this problem but I had my own bad habits: chief among them was the tendency to go into the convenience store when buying gas so I could ALSO get poptarts or granola bars. So when I jumped back on the McDougall wagon I made an agreement w/ myself that I would no longer enter the stores. I pay at the pump and honestly haven't been in a convenience store in 2 years!
If you are in the car a lot or you really feel the need for a drink when you are, make sure you take a bottle of water (preferably filled at home, as water bottles are a terrible source of pollution!) with you wherever you go. Drink THAT instead. Add a little lemon juice if you need a bit of taste. Never leave home without it.
Restaurants may be the hardest for you, but you'll already (hopefully) be ordering ONLY McDougall legal meals so it can't be THAT much harder to order a McDougall legal drink, right? I.e., water. And they will usually bring you lemon wedges if you ask.
The key really is to JUST SAY NO. Stop reinforcing yourself w/ a sugar rush for doing the wrong thing--it's simply IMPOSSIBLE to break a habit that way, as we will keep doing what gets reinforced. On the other hand, behavior that is NOT reinforced--that is ignored--will eventually die out.
Let this die!