Best if the weather is dry and warm. You'll need a warm, dry, well-ventilated place (e.g. airing cupboard, loft, sunny windowsill)
Lay slices on a mesh rack (or thread onto string like a garland, leaving space between slices).
Keep them in the warm, airy spot out of direct damp.
Turn occasionally to prevent sticking and mould.
Drying time. Usually takes 2–4 days, depending on humidity. Mushrooms are ready when they’re crisp, not bendy, and snap when broken.