I think of chopped salad as a combination of three components: the salad greens mixture, the dressing and the add-ins.
The greens may be a combination of a lot of interesting lettuces or just a simple romaine or iceberg. Humble iceberg lettuce takes on a whole new dimension when chopped into a salad. Fresh baby greens are so perfect and interesting that I prefer not to chop them, preparing them instead with chopped ingredients in the dressing.
Dressings can be a bit tricky, as the proportions of oil and vinegar have to be more precise. I have ruined many salads by thinking that I could just "wing it" with the dressing.
The add-ins are a great way to be creative. You can add all kinds of different flavors and textures to your chopped salads with crunchy nuts, sweet raisins, sunflower seeds… whatever suits your tastes. Just remember to jot down your favorite combinations, so that you can re-create them next time.