Keep it out of prolonged water, dry it promptly if it does get wet, and oil it once or twice a year with a food-safe mineral oil or a proper wood finish. Wood moves with humidity, so the enemy is soaking and drying cycles rather than occasional dampness.
Wood absorbs and releases moisture, swelling and shrinking as it does. That is why a wooden handle can sit slightly proud of its bolsters in a humid summer and flush again in a dry winter. It is normal on traditional construction.
What is not normal is cracking, and that comes from extremes: a soak followed by fast drying, or storage somewhere very dry and hot.
Wipe after use. If it got wet, dry it and let it finish drying at room temperature rather than near a heater. Once or twice a year, wipe on a little food-safe mineral oil, let it soak in for twenty minutes, and buff off the excess.
Never put a wood-handled knife in a dishwasher. Heat and detergent will destroy the finish and often the wood.
Stabilized wood has been impregnated with resin under pressure and behaves much more like a synthetic: it barely moves and needs almost no care. Natural wood needs the routine above.
See restoring oil to a dry wood handle if yours has already gone pale and thirsty.