Mushrooms are so porous that if they are exposed to too much water, they will quickly absorb it and become soggy. Therefore, the best way to clean mushrooms without sacrificing their texture and taste is to clean them using minimal, if any, water. To do this, simply wipe them with a slightly damp paper towel or kitchen cloth. You could also use a mushroom brush, available at most kitchenware stores.
If using the whole mushroom in a recipe, simply slice off the very bottom of the stem, which is usually a bit spongy. If your recipe only calls for the caps, gently break off the stems with your hands and discard (or save for making soup stock).