Don't go to the mall or other stores where you'll be tempted. For me, in particular, I must avoid World Market.
Learn
Learn to be satisfied. Volunteer your time or talents.
Something that helped my financial perspective a lot when I was 17 and 18 was working with the orphans and homeless in Argentina with Mother Teresa's Missionaries of Charity. It's hard to complain about not having the latest phone "like the other kids" when you see such deprivation, hunger and need.
Contribute
Help out. It's good for the community, good for you, and good for your budget when you become more satisfied with what you already have.
Keep Off
Keep the TV off. Cancel cable. You save on that monthly bill. It also keeps marketing out of your home by a significant amount. No commercials to overhear. No suggestions that you'd have a better day if you had a tastier cold brew, a plumper mascara, a newer car. Turn off all those commands to go buy something in order to be happier.
Catch Yourself
When you say "I want", catch yourself. When you say, "I wish", stop yourself. Pause. And change your thought process. Can you instead right that minute tell yourself three things you're grateful for instead of focusing on the next thing you want.
Delay
You think you need the latest shoe from your favorite label? See if you can delay buying it for one week. Give yourself one week to get distracted by a different want. By the end of that week, it is likely, you'll have moved on. Resistance is most essential in those first moment and days of the desire. Desires fade and get distracted by the next marketing magic.
Nature can do wonders for resisting marketing's temptations. Going for a walk to your mailbox or around the block or for a walk around a nearby lake. It doesn't have to cost a penny, but it can bring calm and contentment that no "purchasing high" can give or sustain.
Rest
When we're exhausted, buying something feels like it will fix our exhaustion or anxiety. Rest instead. Take a fifteen minute nap and then reconsider the "need" you'd felt for the purchase you wanted to make.
When you want, pause and consider someone more in need. When you think some version of "but everyone else gets to," consider those who don't get to, consider those who have less.
Focus on the Freedom
The freedom that comes with debt-free living, the sense of security and assurance are so valuable and feel luxurious; don't underestimate that or undermine it by capitulating to the tyranny of your next want. Generally our wants, the urgent "needs" we have when considering an advertisement on TV or in a magazine is going to be a forgettable purchase, something that won't be remembered even by us in a month. Save for the unforgettable spending - what is that for you?
You can do this! It is worth it! Building wealth and a legacy for your family is so much more empowering than caving to the impulses we all feel all throughout any given day jammed with marketing that assaults us on all sides. Keep your eye on the goal! You've got this! Stick with it! Each effort, each self denial in pursuit of this goal, your future self will thank you for!