The only thing that works for me? Reminding myself that I *can* have it if I want. I mean, there's no big bad daddy or mommy telling me I can't have it, right? I can have it if I choose to have it -- I mean, come on, someone would be a big enough dumb-ass to lend me the money, right? I just have to be willing to make the tradeoffs -- I force myself not to look just at the awesomeness of the greener grass, but also what it would actually cost me, both financially and otherwise.
We went though this (sort of) when they redistricted our schools and we ended up on the "wrong" side of the line, and then there was this new development with big new shiny homes in the best part of town. I had major house lust -- went and toured the models, looked at the lot layouts, totally fixated myself on it. And then I also thought about giving up my 2.875% 15-yr mortgage, which we are already a few years into and which will be paid off by the time we plan to FIRE; I looked at the extra cost of the new mortgage and taxes and thought about how that would feel in our budget; and most of all, I made myself think through how it would feel to permanently leave the home we thought was our forever home and had remodeled just the way we like it, all to start over again in some generic cookie-cutter version with like 1/4th the yard. And I realized that while I wanted the pluses of the new place, I didn't want them enough to give up what I have now.
Note that sometimes, though, the answer is yeah, I really do want that (for ex, DH and I spend too much on nice restaurants; I looked at our restaurant spend and multiplied by 25 and decided that, yeah, I am willing to work long enough to save that much to live that way forever). And sometimes that analysis makes it clear that there is a problem with my current situation, but that there is another solution short of throwing in the towel that gets me 90% of what I want for 10% of the cost (e.g., we solved our closet dilemma by turning a full downstairs bath that was never used into a half bath with two closets where the tub had been).