Start with fresh mushrooms
Wrapping them in a paper towel and then storing them in an open plastic bag (to prevent condensation from building up) might lengthen their shelf-life another day or so but can also darken the surface of the mushrooms.
When to wipe
Especially if you'll be eating the mushrooms raw (and they are not very dirty), it’s best to simply wipe them clean with a slightly damp towel or a soft brush. Rinsing them with water, on the other hand, can leave the surface of the mushroom slightly slimy—not a texture you’d want in a raw mushroom.
Dry mushrooms well and use soon thereafter
Trim the stem
Most other mushrooms, including white button, crimini, morels, portobellos, can be trimmed close to the base of the stem.
If you are stuffing the mushrooms, and therefore need to remove the stem entirely, reserve the stem for stock or chop it up and add it to the stuffing.
Removing gills and peeling are optional
Mushrooms don’t need to be peeled except for cosmetic purposes.