Dietary iron comes in two forms. Heme iron, found in animal foods such as red meat, poultry and fish, is absorbed relatively efficiently. Non-heme iron, found in plant foods such as beans, lentils, tofu, leafy greens and fortified cereals, is absorbed less well.
You can improve non-heme absorption by pairing it with vitamin C (citrus, peppers, tomatoes), while tea, coffee, and calcium at the same meal reduce it. See foods high in iron for how to build iron-rich meals, and iron supplements when food isn't enough.