1. The 3 bite rule - first to see what it is, 2nd to taste, 3rd to decide if they like it. They ONLY have to take those three bites then if after the 3rd bite they *really* dont like it, fine. (Usually they will end up deciding it doesnt taste as bad as they imagine it to be)
I also use the "how old are you = how many bites you need" rule sometimes.
I have had to learn to feed my son in the afternoon right around 3 or when he gets home from school, or else he'll all of a sudden be starving at 4:30 and eating while I'm fixing dinner then of course he isn't hungry for dinner. So, *make sure* he eats a fairly hearty & healthy afternoon snack an hour to two before dinner. Then no snacking in btwn.
I also have this rule, which has worked really well with my 6yo- he *has* to eat his dinner if he wants to get any dessert. He'll eat his dinner, then get a dessert before bedtime. Or he'll not eat his dinner, then at bedtime the automatic "I'm hungry!" comes up so ok, here's your dinner, you can finish it. (but no dessert, since dinner is dessert when eaten at that time)
We kinda implemented these in stages, first was either the age and/or the 3 bites to see/taste/decide rule.
I think the 3 bites to taste/decide is effective because 1- they're more willing, I think because they feel more in control with the assurance that once they've had the series of bites to decide they really dont like the food, they dont have to eat any more of it. It puts them in control, which is where they want to be, but you are satisifed that he's tasted it and gotten past the prejudice of his LOOKING at it and deciding it's 'yuk.' After all 3 or 4 bites of a veggie or whatever it is for a 4 yo is pretty good. And it gets them used to new foods that later on he'll be more used to it then more accepting and willing to eat/like it.
Another thing my sister said (her kids are so very picky tho... mine's not!) was to make sure there was at least one "good" food that they'd fill up on at each meal - ie, a roll, or plain noodles which you know they'll eat when you're serving something they may or may not like. Moms feel better when the kids have at least eaten SOMEthing. We're glad our son is a better eater, he may not eat MUCH but he eats a good variety of foods.
And last but not least- DIPS! dressings, ketchup, etc. My son will eat all the rice he can hold if I let him have it with cinnamon sugar on it. Or dip into ketchup or dressing or whatever. I saved a couple little plastic cups (from frosting that come in the refrigerated cinn/orange/etc rolls, or maybe the scoop from lemonade/drink mixes? etc) Either those little cups and/or put directly on their plates, and they have fun dipping their green beans into dressing or potatoes into ranch dressing or meats into whatever it may be. They have fun with their food and will eat more of it that way!