If you want a really eye-opening exercise, try this. Next time you decide to stop for fast food, like McDonalds or whatall, (or think you're really "craving" it), make a conscious effort to sit and look at what you're actually eating. Ideally, take it home, unwrap it all, and place it on a proper plate (though you can get a similar effect by laying it out all out on the sandwich wrapper, if you're on the run). A couple years ago I did this with a double cheeseburger combo, so I'll use that as an example. Really look at this meal you "crave" - if you place a fast food cheeseburger and fries on a plate and actually look at it, instead of eating it out of the wrapper/bag, it's really not that appetizing! At all! The cheeseburger usually looks a little slimey and squished, and the fries are nasty compared to nice fresh fries at a pub or restaurant. If you go even further and dismantle the sandwich, peeking at the meat itself, it tends to kill the appetite rather than enhance it!
I've done this and similar "analysis" steps for fast food and other "forbidden" stuff. It's part of the whole idea of "mindful" eating, but it really works for me - once I really took a look at what fast food actually is, I really don't have a whole lot of desire to go back there. If I want a burger, I have a burger - but I'd rather have something that really tastes good over a greasy fast food option. I try to make the effort to eat/order what I would like, but I make the effort to not eat unhealthier foods unless it's really good - if I order a sandwich and fries and the fries are soggy or cold or otherwise bad, I don't just eat them because they're there (which I used to do).
It's worth a try, especially if you feel you're struggling with "losing" or "restricting" certain foods - sometimes we build up something that's off-limits into this fantastic ideal, and if you actually consider what you're looking at it's pretty unappealing! I've never been one for fake mind games ("imagine that ice cream glommed onto your butt" - yeah, I still want it!), but if I actually observe whether something is really palatable or not, it's easy to call up those images the next time I get an impulse to try it again. I'm not saying I'll never eat fast food again, but I really couldn't care less if I do. There are plenty of other foods that are much more worthwhile.