For skin, apply a few drops to an area that feels dry or rough, then spread it thinly rather than adding more immediately. It can be used alone on body areas or added to an existing face or body routine. If using it on the face, begin with a patch test and apply sparingly, because the product information describes the oil as concentrated and reactive skin may not tolerate every plant oil equally.
For hair, the most practical method is to apply a small amount to the lengths before washing. Focus on the mid-lengths and ends rather than the scalp if your main concern is roughness, dryness in appearance, or lack of smoothness and shine. Leave it on as a pre-wash oil treatment for a short period that suits your routine, then shampoo thoroughly. If your hair is fine, start with less than you think you need; if it still feels heavy after washing, reduce the amount next time.
Because this is black cumin seed oil, it has a characteristic aroma. If you are sensitive to scents, try it first on a small area or in a limited hair application before using it more widely.