A simple balsamic vinegar salad dressing, and ideas on green and radish salad mixes.
Use extra virgin olive oil, or include other oils, such as grapeseed and walnut oil. Look for cold pressed oil.
Strong olive oil and balsamic vinegar do not mix well. Use mild, fruity olive oils with balsamic.

Vinegar is usually 20% to 33% of the total dressing volume.
Experiment to find the right brand of balsamic vinegar. For salad dressings, low cost commercial balsamics are perfect.
Mince the garlic and mix into the oil, and rest for at least several hours to remove the harsh garlic edge. The oil should be used within several days or refrigerated, as garlic will go rancid.
Other possible additions include salt and fresh ground pepper, herbs, mustard, or minced shallots.
Pre-made salad mixes from stores often include unwanted vegetables or go bad quickly, though will save time. I start with a base of red lettuce, and add other dark leafy vegetables, like spinach or radicchio. To make leafy vegetables last longer, clean them, then soak in cold water for 15 minutes. Spin the vegetables until mostly dry, pat them down with paper towels, and refrigerate.
Include a small amount of crushed walnuts for healthy fat. Other common additions include croutons or Parmigiano Reggiano cheese.
Add small amounts of the dressing and mix until the vegetables are lightly coated. This method avoids overdressing the vegetables.
For a salad with more texture, use carrots, radishes, cucumbers, and daikon. Cut the vegetables using different methods. For example, carrots and other long vegetables can be cut at an angle, rolled 180 degrees, and cut again.