Act as a certified personal trainer with 10+ years of experience specializing in bodybuilding and strength training. Provide a detailed, step-by-step guide on the best exercises to develop strong and well-defined pectoral muscles for [BEGINNERS/INTERMEDIATES/ADVANCED] fitness levels. Include [3-5 SPECIFIC EXERCISES] such as bench press variations, flys, or push-ups, along with their proper form, recommended sets, reps, and rest intervals. Address common mistakes and how to avoid them, and suggest modifications for individuals with [SPECIFIC LIMITATIONS, e.g., shoulder injuries or limited equipment]. Additionally, explain how these exercises target the upper, middle, and lower pectoral regions for balanced development. Finally, recommend a weekly workout frequency and tips for progressive overload to ensure continuous muscle growth.