Final answer:
To prevent a hematoma, apply direct pressure until the bleeding stops, and a cold compress can be used to reduce swelling and pain.
Step-by-step explanation:
The best way to prevent a hematoma after an injury is to apply direct pressure until the bleeding stops. This helps to curtail further bleeding and allows the blood clotting process to start, which is essential for wound healing. Applying a cold compress can also be beneficial in reducing swelling and pain. Elastic bandages may be utilized to provide compression and help in maintaining clotted blood under the skin to prevent hematomas, especially in cases where long periods of standing or after certain injuries might cause swelling.