What mistakes should beginners avoid in digital marketing?

I recently started a small food delivery service called QuickBite Home Kitchen, and I’m learning digital marketing step by step. While researching agencies, I found Cloud innovators solution, but I also want to understand common beginner mistakes before spending money. Should I avoid running ads too early, or is poor targeting the real issue? If experienced marketers could share what mistakes cost them the most in the beginning, it would really help me plan better.