Vinegar: There're quite a few choices out there, white wine vinegar is the most obvious choice of all, red wine and balsamic are great alternatives; don't forget Cider vinegar if you're aiming for a special fruity flavor.
Oil: Any vegetable oil would do, really, for a basic vinaigrette, but personally I try to avoid any oil with strong flavors, like walnut or peanut; Good quality extra virgin olive oil is always my first choice, right after, light and neutral flavored oil like corn, sunflower or soybean oil.
Oil:Vinegar ratio should be 3:1, but different vinegar brings different acidity to your mixture, so you might have to adjust, and don't taste your vinaigrette straight, dip a piece of lettuce or something.
Lemon Juice is good as seasoning, but no alternative to vinegar; Olive oil and lemon juice are a good combination for summer salad, that's no vinaigrette. Honey will not only bring sweetness to your mixture, it will add thickness to it too. Dijon mustard will take your vinaigrette to another level, but emulsify them is by hand is tricky.
And it's really common sense that oil and water don't mix, but here's why.
The reason for this mutual repulsion is electrical. Water moleculesare electrically unbalanced, or polar: each has a slight positive charge around the oxygen atom and partial negative charges around the two hydrogen atoms. Water molecules thus tend to stick together because the negative end of one attracts the positive end of another. But oil molecules, being nonpolar,don't interact nearly as well with water as water mingles with itself. Infact, scientists refer to fats as being hydrophobic-water-fearing.
If you try to overcome this natural repulsion by stirring very hard, you will divide the oil into finer and finer droplets. But those globules won't ever truly dissolve in the water. To the naked eye, it may look as though they mix because the suspended droplets can become microscopic.
Vinaigrette is perfect example of Water-in-Oil emulsion, for Oil-in-Water emulsions, there're Cr