JELL-O TIPS The Jell-O recipe developers offer these suggestions for making it right every time: To double recipe, double the amount of gelatin, liquid and other ingredients used except salt, vinegar or lemon juice. For these, use 1.5 times amount given in recipe. ' To store prepared gelatin overnight or longer, cover before refrigerating to prevent drying. Always store gelatin desserts in the refrigerator. When adding fruit or vegetables, first chill gelatin until it has thickened. Otherwise, fruit and vegetables will either float or sink. Do not use fresh or frozen pineapple, kiwi fruit, figs, mangoes, guava or papaya, or fresh ginger in gelatin. All contain an enzyme that keeps gelatin from setting. All are fine if cooked or canned. Generally, gelatin molds are best served right from the refrigerator. A gelatin mold containing fruit or vegetables can remain at room temperature as long as two hours. To shorten the time it takes for gelatin to set, use a metal bowl or mold rather than glass, plastic or china. Metal chills more quickly.