Layering a cocktail is really very simple. Once you have ascertained the specific gravity of each spirit, just begin with the heaviest spirit on the bottom and layer the rest of the ingredients in order from heaviest to lightest on top of each other. A good tip to remember is to pour each ingredient slowly over you bar spoon as it rests against the glass. That way they do not break through the previous layer. It also helps to chill or freeze each liqueur before use.
1 oz St. Germain Elderflower Liqueur
1/2 oz creme yvette
pour the St. Germain in a small aperitif style glass
gently layer the creme yvette over the St. Germain