Remove sails and other gear so that air can circulate and moisture/mildew inside the boat can be avoided. Use the mast as a ridge pole. If you use the cheap blue plastic tarps, tie them down carefully with shock cord, not rope, so that the wind won't rip the grommets out. A good canvas tarp which will breath is best, but they are heavy and expensive. Some people tie quart milk bottles of water to the tarp to hold it down.