Magnesium oil typically is sprayed or rubbed directly on skin. Using 1 ounce or more daily offers the most effective approach because it permits full concentration of magnesium oil to penetrate skin and build tissue magnesium levels. However, direct application sometimes causes stinging or burning sensations. The body usually adapts quickly to these sensations (so they do not feel so intense), especially if the product is a high-purity one like Ancient Minerals magnesium oil derived from undergound seabeds (rather than ocean water-derived magnesium oil). You can spray your entire body, but avoid sensitive areas, including eyes.
If the burning or stinging of magnesium oil is too much for you, then dilute magnesium oil 50-50 or more with water. Some people add magnesium oil to their favorite skin lotion or make their own lotion. Such a lotion might be 1 part magnesium oil, 1 part coconut oil, and 1 part aloe vera gel. Another option is applying the oil and waiting ten minutes for it to absorb into skin, then wiping the remainder off using a wet washcloth.
Magnesium baths are effective, too. Add magnesium oil to bathwater, or use magnesium flakes, or use both. The flakes are very cost effective. You can find ancient minerals magnesium flakes online. Take a warm bath, but not a hot bath. A hot bath will encourage perspiration and excretion from pores. A warm bath will open pores, but also encourage absorption of the magnesium from the bath water. You can even reuse bathwater (if it is clean), or just soak your feet in it.
Another useful form of magnesium chloride is magnesium gel. This may not be quite as effective at raising tissue concentrations of magnesium as using direct magnesium oil (since the gel appears to "hold" the magnesium so it absorbs into skin more slowly, but many users swear by the gel for skin conditions (e.g., psoriasis). This may be an instance where holding more magnesium at the surface of contact supports skin health better than if it were rapidly absorbed into muscles and other tissues beneath the surface layer of skin.