Nikon F3 - Manual (Page 64)

2, Clean the inside of the camera.
Brush out the inside of the camera periodically using a soft brush.
Do not exert pressure on the shutter curtains as this may damage them.
Also keep the mirror free from fingerprints and dust.
Store the camera properly.
Store the camera in a carrying case to protect it from dust. Avoid
storing the camera in excessively hot, cold, or damp places. Always
attach a body cap to the camera body and a front and rear lens cap to
the lens when storing them to prevent dust from getting inside the body
or on the lens surfaces. Remove the batteries before storing the camera
for an extended period of time.