One step that I have taken over the past couple of years is to write down all of our purchases...from groceries to gas...monthly. I put off doing it for a long time, because I just didn't want to have to do it. Now, every few days or once per week, I just go through our purchases and note them under the corresponding category. My budget lists how much I have allotted to each category, so I can easily see how my purchases are adding up.
A further check is to go back at some point(s) (now is the perfect time) ;) to look over each of those purchases + to assess what I think of them months later. Have I realized that I really didn't need that thrifted button down shirt? It was a good price + it fit well + I really like it...but it doesn't really serve a need in my closet...and it's already in the donate pile. Since I'm trying to send as much money toward our mortgage as possible, those dollars would have served a more lasting purpose there.
It can be tough to forgo each + every "treat" along the way...and I really wouldn't want to do that...but some turn out to be better than others. Noticing that disappointing purchase helps train me mentally to avoid the next one.
Revisiting purchases...it's a good thing.