What are the biggest SEO mistakes beginners make?

In your opinion, what are the biggest SEO mistakes beginners make when starting a new website?

What advice would you give to someone who is just getting started to help them avoid common mistakes?

I think the biggest mistake is expecting results too quickly. A lot of beginners jump from one strategy to another before giving anything enough time to work. I'd focus on solid content, good site structure, and learning the basics before worrying about advanced tactics.