I like to make mine in a mason jar. I measure it all into the jar and then just shake it up vigorously until the oil and vinegar start to emulsify. I also reshake before each use.
To add variation from there, here are some suggestions:
Fresh Goodies: If you know that you will be using the dressing quickly, you can add fresh herbs and vegetables like diced scallion, garlic, parsley, or basil. Fresh herbs will shorten the shelf life so I will make a batch I can use quickly or put the leftover in the fridge, knowing that it will harden and will have to come to room temp for reuse.
Shelf Stable Goodies: If you want to make a large batch to keep handy on the counter for use over several weeks, you can safely add dried herbs. Try dried herbes de provence, oregano, onion powder, granulated garlic, coriander, sage or cumin. The herbs you add can change the direction of the food style so think of salad style you are targeting and match the flavors appropriately. For example, I love a tart herbacious vinaigrette on a cold green been and potato salad. The herbes de provence work well here. In chilled steamed veggies like carrots and cauliflower, a little cumin or even curry seasoning works very well.
A Little Heat: You can add a little heat by mixing in some wasabi powder, a few dashes of tobasco, chili powder or dried chili flakes. These variations are great on greens with seared Ahi or a tortilla salad with beans, sharp cheese and cilantro.
A Little Sweet: Classic vinaigrette is very tart. To balance the acid, try a few tablespoons of artisanal honey (I love buckwheat or avocado) or some naturally sweet enfuso balsamic vinegar. This approach is especially good on delicate greens like butter lettuce, or red and green leaf.