Using a good serum incorrectly can make your skincare routine unnecessarily complicated.
In many routines, serum is applied after cleansing and before moisturizer. This allows the serum to be applied directly to clean skin before heavier products.
A basic routine can be:
Cleanser → Serum → Moisturizer → Sunscreen
If you use several serums or active ingredients, the order can depend on their formulations and the manufacturer's instructions.
You do not need to use a large amount of serum. Applying more product does not automatically produce faster or better results and may increase irritation with certain active ingredients.
Most importantly, give your routine time. Constantly changing products can make it difficult to determine which ingredients are actually helping your skin.