Act as a certified physical therapist with 10+ years of experience in musculoskeletal rehabilitation. Provide a detailed, step-by-step guide on the best exercises to relieve neck pain, tailored for [BEGINNERS/INTERMEDIATE/ADVANCED] users. Include [STRETCHING/STRENGTHENING/RELAXATION] techniques, explaining the proper form, duration, and frequency for each exercise. Also, address common mistakes to avoid, such as [OVEREXTENDING/TENSION IN SHOULDERS/POOR POSTURE], and suggest modifications for those with [CHRONIC PAIN/INJURY HISTORY/LIMITED MOBILITY]. Use clear, actionable language and emphasize safety and gradual progression.