Common mistakes when using aluminum foil in cooking include: 1) Using foil that's too thin, leading to tearing during cooking. 2) Not allowing for proper air circulation, which can result in uneven cooking or steaming instead of roasting. 3) Wrapping foods too tightly, which can prevent even cooking and may cause the foil to stick to the food. 4) Using foil with non-stick coatings on the inside, which can flake off and contaminate the food. 5) Overlapping the foil edges, which can cause food to leak out. 6) Not using enough foil, which can lead to spills and messes in the oven. 7) Not preheating the oven before placing foil-wrapped foods inside, which can lead to uneven cooking. 8) Not greasing the foil before placing food on it, which can cause sticking. Proper use of aluminum foil can enhance cooking and prevent these issues.