I would proceed with making any changes to your diet slowly and incrementally, or in other words do NOT make radical changes.
You could start with documenting your current eating habits. Track your meals and calories by using a journal/notebook or use an online/mobile journal like MyFitnessPal.
Review your journal after two weeks and look at possible foods that you can target to either add, eliminate, or replace. Commit to making these changes for approximately 1-2 weeks until you get the hang of it. After that time frame, review again and target the next series of changes. Feel free to adjust the amount of changes you make (i.e. more/less) based on how well you managed during the last period. Of course you are still tracking your meals, right? :)
Replace: Instead of snacking on potato chips, I will eat a handful of almonds.
Add: I will eat an apple and/or a banana every day.
Eliminate: I will stop eating double-cheeseburgers from Hamburgers 'R Us.
Focus on having good, well-rounded core meals, meaning breakfast, lunch, and dinner. Eating properly may reduce your snack cravings.
If you catch yourself snacking at various points of the day, try to ask yourself WHY you are snacking.
Are you bored, stressed, depressed? When you smoked you may have formed unconscious desire to smoke at certain times or as a response to certain stimuli. For example, I've seen smokers light-up after every meal or every time they answered the phone.
Once you become aware of these habits you can tell yourself "NO" and choose a better alternative, like a glass of water. Over time you'll re-train yourself to automatically go for snacks that won't increase your waistline.
10 Appetite Suppressing Foods
I've included a list of 10 appetite suppressing foods from Men's Health to give you some snack ideas. Note this isn't a panacea but you may find that snacking on these may make you feel less hungry:
Apples, Flaxseeds, Caffeine, Water,
Hoodia, Chicken & vegetable soup,
Wasabi (spicy foods), Oatmeal, Salmon,