After a long and careful study of what makes a good salad, I have decided upon three key components, in addition to your standard greens and veggies:

1. Something sweet (like dried cranberries, raisins, pomegranate seeds, chopped apples, etc.)
2. Something crunchy (like croutons, crushed pita chips, tortilla chips, nuts, etc.)
3. Cheese (depending on the salad, goat cheese, feta, and parmesan are all good choices)

Of course you must use these things in moderation to avoid overdoing it and adding too much fat/calories/etc to a dish that, essentially, is supposed to be a healthy addition to your meal.

More on salad dressing after the jump.

A good salad dressing is also important for a good salad. And I believe that making your own dressing is tasty, easy, and fun. Here are some tips:

1. You'll need a jar to mix your salad dressing in. Any jar or tupperware where you can close it and shake without risk of spillage will work just fine. I know some dressing recipes call for whisking and all that, but I've never had a problem just giving it a good shake. Just add your favorite combination of ingredients, shake until blended, taste, adjust, shake again, and voila!

2. Start with a solid base - something to give your dressing body and add volume (to balance out later additions of acid, like vinegar). If you already have pre-packaged salad dressing at home, this can be a great start as it likely has one of these "base" ingredients and is probably spiced. If you don't have pre-made salad dressing, never fear. I think you can make an equally good (if not better) dressing by starting with things you already have in your kitchen. On the sliding scale of little fat to lots of fat, consider:
Orange Juice
Plain Yogurt or Sour Cream (non-fat varieties being less fattening, obviously, than otherwise)
Olive oil
Low-fat or olive oil-based mayonnaise
Full fat mayonnaise (creamiest, but also most fattening)

3. Add some vinegars or citrus that you like - add about 1/4-1/2 the amount of base (so for 4 tablespoons oil, 1-2 tablespoons of vinegar). Balsamic is one of my favorite vinegars. Rice wine vinegar or apple cider vinegar adds a touch of sweetness. Lemon or lime juice is also great - lemon juice works well in Greek/middle eastern recipes and lime juice works great in southwestern recipes and some southeast asian recipes.

4. Add something else to give flavor - like mustard, pomegranate syrup, honey, soy sauce, peanut sauce, salsa, hot sauce, etc. These are things that allow you customize your dressing to the particular cuisine or style of salad you're making.

5. Toss your salad and enjoy. Custom-made dressings tend to last as long as the individual ingredients that you put in them. So, really, given the range of ingredients I described here, pretty much forever in your fridge. But, as with most foods, I'd eat it within a week or so.