To be a rock star .NET developer, one should have an impressive technical background such as a computer science degree or .NET certification. It is also important to have experience handling various projects and demonstrating communication skills like clearly sharing ideas. Additionally, recruiters look for passion for .NET development and flexibility in terms of working extra hours or making changes to projects. The key qualities a .NET developer should cultivate are an impressive technical skills, experience with projects, strong communication abilities, passion for the field, and flexibility.