I just puke a lot. It gets better with more time at sea. Avoiding breathing noxious exhaust helps me a lot too, that's quite a trigger. Don't go below deck when under way. Don't try practice tying knots or reading books under way, all the usual motion sickness triggers to avoid in cars/trains. Watch the horizon/scenery, man the helm if you can, have the wind on your skin.

Short day sails are kind of the worst because it's enough to get sick, but not long enough to get over the "sea legs" hump.

Do overnights, long weekends, sleep/live on the boat. That helps me significantly.

I haven't tested this on the boat yet but fasting seemed to help on my last cross-country train trip. It's on my list of things to try sailing. Fasting is basically being deep in ketosis AIUI, so maybe just going sailing on a keto diet would make a difference. I was _trying_ to make myself motion sick on that train trip where I hadn't eaten for 48hrs, and there wasn't even a hint of nausea, it's a very different head space.