It might help, or not (each case is different), but this is what we do:
We do allow fresh fruit and veggies ANYtime, even 5min. before dinner, even if it "spoils" their appetites. How do you spoil an appetite with healthy food? I consider it equivalent to the "salad" that some adults eat at the beginning of dinner. Fill up on the healthy, have less room for the sugary/salty/starchy -- it is a great deal! If they get hungry 5min. after dinner -- guess what snacks might just be available?
We rely on the power of hunger, and the kids' desire to be self-sufficient. Baby carrots and "broccoli feet" (the stems) taste delicious when a kid (or myself) is hungry. I leave acceptable snacks in the fridge or on the kitchen table, such as veggies, nuts, cheese sticks, or sliced fruit, and the kids love to wander in and help themselves. Note, this became easier after I cleared out the fridge crap -- the chocolate yogurt, the leftover cake, the chocolate milk, the lemonade. Now, unless they want to dig into the squash casserole, baked beans, or the raw onions, they have to pick snacks I leave for them. But they have choices. And they know that, if they don't finish what they started, they need to put it back in the fridge so it doesn't spoil.
(Side note -- I loathed being in the kitchen around the clock, serving kids and cleaning up after their crumble-making butts. I used to spend my WHOLE day there, either prepping, feeding or cleaning up, then the cycle would start all over again for the next meal. I do want them to be nourished, but I have no desire to be their waiter for 12 hours out of 24, especially when they didn't get hungry simultaneously. Snack-wise, they got self-sufficient when the oldest was three or four, and got strong enough to pull the fridge door open. Now, we have time for counting games and reading books, and if it's not a designated meal time, they take care of their snacking by themselves, then come back to play or read.)
Additionally, when I cook something "iffy", I involve them in the cooking process. Not to say that they clear their plates as a result (I wouldn't want them to feel like they have to anyway), but it increases the chances of them taking a bite from that squash casserole or the baked chicken-and-salsa. If nothing else, we do the guess-the-spice game (for example, they can smell rosemary when it is fresh, but can they recognize the scent on the baked potatoes?)
I guess I want them to be fed, and be adventurous about food. When they turn their noses up at some new dish, I encourage them to at least SMELL it. A kids' nose is finer than that of an adult, anyway. Because much of our appetite is aided by the sense of smell, I consider the sniff test to be the first step, instead of the obligation to take a bite. (As an adult, if something smells repulsive to me, why the hell would I want to take "just one bite, one single bite, dearie?" Conversely, if it looks ugly but smells like heaven, like some casseroles do, I might be tempted into tasting it.)
HTH. As they say, your mileage may vary. Good luck to you!