Since you are guaranteed to make mistakes out there, why not learn vicariously from other thru-hikers in order to limit your learning curve.
Thru-Hiking Appalachian Trail Conservancy
5 Mistakes Most Beginner Hikers Make (How to Avoid Them)
Thru-Hiking Appalachian Trail Conservancy
11 Things I Wish I'd Known Before Hiking the Appalachian Trail
TrailBuddy
A Thru-hiker's Guide to Hitchhiking
How to pack a backpack for hiking
Top 10 Mishaps to Avoid When Hiking the Appalachian Trail – AppalachianTrailClarity
Nimblewill Nomad' Becomes the Oldest Person to Hike the Appalachian Trail - The New York Times
How to Thru-Hike the Enchantments — The Grah Life
From Georgia to Maine: What I learned on a 6-month hike along the Appalachian Trail - The Washington Post
Hike Strong: Mental Training for Long Days on the Trail - Wildland Trekking
Not for novices: America's most dangerous hikes
12 Mistakes to Avoid on Your First Multiday Hike, According to Experts