Skipping the Emulsion: Without proper emulsification, your vinaigrette can separate and feel greasy. To avoid this, either use some electronic assistance in the form of a food processor or high-powered blender ~OR~ whisk the vinegar with the seasonings first, then slowly add the oil while continuously whisking until the mixture is cohesive and slightly thickened. 2. Using Low-Quality Ingredients: Since vinaigrettes are made with just a few ingredients, each one counts. Using low-quality oil or vinegar can result in a flat or unpleasant taste. Opt for good-quality extra virgin olive oil and fresh, flavorful vinegar to ensure your dressing sings with flavor. 3. Overdoing the Vinegar: Start with a lower ratio of vinegar to oil (like 1 part vinegar to 3 parts oil), and adjust to taste. 4. Forgetting to Season: Just like any dish, vinaigrettes need seasoning to enhance their flavors. Always season to taste and remember that a little goes a long way!