Kicking the soda addiction, as you put it, was my first step to eating healthier. I used to (no joke) drink one-two 2-liter bottles of soda per day which makes me feel nauseous just thinking about.
Then it was fast food because that was a prime way for me to get my soda.
After some time, you will begin to crave healthier foods instead. Your taste and desire will change.
That's the first thing I would stress as a motivating factor; just know that eventually you will enjoy other drinks given enough time.
What helped me get over the initial cravings were fruit juices (100% juices; not the cocktails).
Also, I cut down on my selection of soda. For instance, instead of drinking Pepsi, 7UP, Dr. Pepper, Sprite, Cactus Cooler, Coke, and ginger ale, I just allowed myself ginger ale or 7UP.
Not only did I cut back on the selection but the quantity. One, maybe two cans of soda per day at first (which is a substantial difference from 1-2 bottles). Once I adapted to that and substituted in more juices and I eventually dropped drinking the cans of soda too.
Now I rarely even drink soda because it's just too sweet and doesn't quench the thirst.
After I dropped soda out of the diet, I began cutting back on the fruit juices but I still haven't totally cut them out. It's better to eat the fruits as they are so you can get more fiber but the 100% juices aren't as bad as soda. Be careful of how much juice you consume too in the long run.
That's how I was able to do it anyway. Some may have a quicker way of curbing and cutting the addiction but in order for me to stay motivated I took smaller steps and didn't trust most dieting products.
Another motivator for me has been just researching the ingredients in soda and knowing the long-term physical costs. If you are at all concerned about your health and you know what soda can do, you will be more than happy to at least cut back and replace it with a more healthy alternative that hydrates much more efficiently.
Also also, depending on what alcoholic drinks you have, be careful to not let your drink mixes get the better of you.
Again, depends on what works best for you. Some people can just drop a habit over night and walk away from it for good, while others (such as myself) sometimes require a gradual change to something like a new diet.