To properly use an Erlenmeyer flask, ensure that it is clean and dry before use. Gradually add chemicals to the flask, never filling it more than two-thirds full to allow for mixing. When heating liquids, use a heat-resistant mat or wire gauze to prevent direct contact with the flame. To care for an Erlenmeyer flask, wash it with soap and water after use and store it in a safe place away from other glassware.