Salad dressings usually consist of oil, an acid, and seasonings. More often than not, the ratio of oil to acid is 3:1. That means for every three tablespoons of oil you use, you're going to need about one tablespoon of acid.
A basic dressing is simple and painless. Mix:
6 tablespoons extra virgin olive oil
2 tablespoons lemon juice
1 teaspoon of salt
1 teaspoon of pepper
1 tablespoon any variety fruit jam or jelly (optional)
For most dressings, or vinaigrettes, the gold standard of oils is extra virgin olive oil. You can also use canola oil, peanut oil, avocado oil, or sesame oil for an Asian-style dressing.
For most dressings, the gold standard of acids is lemon juice or balsamic vinegar. You can also use any citrus juice (orange juice and grapefruit juice work well) with different vinegars (apple cider or white wine vinegar work well).
Whisk together olive oil and lemon juice until they blend (about 30 seconds). Add salt and pepper. Whisk the jam or jelly into the emulsified dressing (optional). Serve!