Cut the leaves, but keep their shape
I have a horror of salads made with leaves cut into bite-size pieces, a habit that probably evolved in the days when it was considered impolite to eat salad with a knife. If the leaves are cut too small, they lose their distinctive shapes and a lot of their crunch. On the other hand, you don't want to serve giant leaves that won't fit on the plate or that are difficult to maneuver.
Greens with small leaves, such as arugula, basil, purslane, watercress, and young spinach, should be stemmed but the leaves left whole. Larger leaves, from greens such as romaine, large red oak leaf, and escarole, should be trimmed as shown in the photos. Cut away thick, woody stems. Use a sharp knife to slice off stems like those found on arugula and watercress.
To determine the amount of greens needed, figure on about a handful of salad per person; double the amount if the salad is a main course.
Tear large leaves like romaine and large oak leaf along the central rib; they'll retain more of their character.
Trim out tough ribs completely. Fold the leaf lengthwise and gently pull up on the stalk, ripping the rib out as you go.