try and tie all your rigs before you set out,dont look down at the floor of the boat,try and stay out of the cabin if the boat you are going on has one, if your standing up, try and focus on something on the horizon,failing that, boots used to sell something called sea legs, its a kind of travel/motion sickness tablet. try not to drink lots of fluid the night before, because it will slosh around the opposite way to the sea when your standing still.on a hot day though have plenty of water with you as you can get very quickly dehydrated !my only other bit of advice is, if you do start to be sick drink lots of lemonade ,it tastes the same coming up as it does going down !my father was taught to eat lots of oranges while at sea, the deck still bears the stains,good luck and stick with it.