When welding rebar, it's essential to use the correct techniques to ensure a strong and reliable joint. Clean the rebar surface before welding, removing any rust, dirt, or debris. Use appropriate welding positions and techniques, such as the butt weld or lap weld, depending on the project requirements. It's also crucial to use the proper welding rod or electrode, which is compatible with the rebar material. Be sure to follow safety guidelines and wear protective gear during welding.