For a firm base, use thick textured ingredients like Greek yogurt, whipped cream, cream cheese, or custard.
Chill the yogurt, fruit compote, and mousse prior to making the layered parfait so they stay firm.
Juicy fruits contain moisture that can drip out and ruin the layers, therefore before adding fruits, pat them dry or cook until reduced.
Crunchy additions like crumbled granola, cookies, and nuts soaks moisture and keep the parfait dry and stable.
If you are not sure to use the spoon, you can make a makeshift piping bag with milk sachets to maintain neatness when layering the parfait.
Wide jars are a no go for parfait as they result in thin and blur layers, therefore use tall and narrow glass to stack firm layers.
To keep the layers firm until serving, always freeze after adding every single layer and then finally freeze after assembling the whole parfait.