Using high quality fruits. Leftovers and reject fruits fits perfectly for wine making. High quality fruits are the best however. Final wine flavor rely on starting fruit flavors plus those created during fermentation and aging process. No artificial flavors added. Thus prime fruits are best for making high quality wines.
Proper hygiene. Ensure the cleanliness of workplace and production staffs. Any form of contaminant, no matter how big or small, is enough to ruin the product.
Adjustment of must properties. Acidity and sweetness should be adjusted to favorable values. It should be the same every batch. Deviation from set values might have a significant impact on final taste.
Pure cultures and proper room temperature. Different yeast strain have different alcohol output. Choose the right strain. Always ensure the purity of starter culture. Practice the microbiological isolation technique or buy from a reputable source. Performance is affected by temperature. Conduct a strict temperature monitoring and adjustment. Lower by means of air conditioner and increase by means of light bulbs. E.g. Temperature and starter culture requirements of red wine and white wine are different.
Mixing of different outputs. Apparently the hardest to implement. Every finished batch that passed quality check have slightly to significant taste differences. Fruits from high altitude place might have better flavor. Fruits from nutrient rich soil might have better taste. Subject each batch to panel of expert wine tasters. Then the final wine is made by mixing portions from several batches. The proportion is decided by the expert panel.