Ingredients are listed in descending order of concentration, down to 1%. Below that, they can appear in any order.
The first five
These usually make up most of the formula. They tell you whether you are buying a water-based gel, an oil, or a rich cream.
Actives by name
Niacinamide, ascorbic acid, salicylic acid: if a product claims an active ingredient, it should be listed. Where it appears in the list gives you a rough idea of how much is in it.
Fragrance
"Parfum" or "fragrance" can cover many compounds. If your skin is reactive, choose fragrance-free formulas for leave-on products.