Layering is a technique whereby the ingredients are layered, visible in transparency in the glass or cup. Once the difference in specific weight of the different ingredients has been identified, they must be gently poured in, starting from the heaviest to the lightest and forming clean layers of different colours.
Check out the suspended coffee
One more tip
If you want to create a top layer of liquid cream (e.g., in irish coffee), you can lightly shake the liquid cream without ice in a cobbler shaker, helping it to incorporate a little air which will lighten its structure, allowing it to float better on top of the drink.