Clean with a damp cloth and dry with a soft cloth.
Solvents (e.g. nail polish remover / turpentine) will damage the surface.
Don't use detergent containing ammonia or bleach (don't use Handy Andy).
Plywood surfaces should not come into contact with anything sharp / hot / moist / wet. Always protect surfaces with coasters or mats.
Changes in humidity will cause wood to shrink or swell. Under normal conditions, small cracks in solid wood are to be expected while extreme changes in humidity can cause warping, splitting and cracking. Regulate humidity where possible.
Extended exposure to direct sunlight will cause wood to fade.
If you feel over time that the surface needs to be sealed again lightly sand with 400-grit sandpaper and seal with a water-based sealer.