It’s not always necessary to mix a vinaigrette, especially if you’re only making a simple salad. An easier way is to toss the salad greens with a little olive oil (enough to make the leaves glisten), then season the salad with a touch of vinegar (like you would with salt) or something else acidic. Toss again and give it a taste. If it’s too acidic, add a little more oil and vice versa.
Don’t forget to add a sprinkle of salt.