The food you are going to deep-fry should be at room temperature. This reduces the drop in the temperature of the oil when you put it in, lessening the chance of splattering. You might want to dry the food with a paper towel before adding it. If the food to be deep-fried is in a sauce, use a slotted spoon to let it drain before adding it to the wok. Similarly, if the food is batter-coated, make sure all the excess batter has dripped off before placing it in the hot oil.