While it's certainly possible to clean your own windows, achieving a professional-level, streak-free finish can be challenging. Professional window cleaners have experience, techniques, and tools (like squeegees and water-fed poles) that make cleaning more efficient and effective.
If you choose to clean your own windows, use a good quality glass cleaner and microfiber cloths. Avoid cleaning windows in direct sunlight, as the cleaning solution can dry too quickly and leave streaks. It's also crucial to take safety precautions if you're cleaning high windows, using a stable ladder and having someone spot you.