Good fruit = good wine. Shitty fruit = shitty wine. See where I'm going...
All of the great winemakers are very selective when choosing their grapes for the best vintages. Grapes are selected on location, flavour, ripeness, acid and tannin levels. All of these things affects the quality of the wine. This should be the same for your Country Fruit Wines.
Of course we might not be able to test for specific sugar, acid and tannin levels in the fruit you want to use for winemaking, but does it taste good? Would you make a pie out of green peaches, or leave stems and leaves attached to the blueberries when you're making muffins? Of course not! Same should go for making wine.
I'll give a few more specific preparation notes below but here's some tips for all fruit brought in for making wine...