Tiered breakdown for The Intelligent Investor by Benjamin Graham:

Most Important

Chapter 8: The Investor and Market Fluctuations - Core concept of Mr. Market and psychological discipline
Chapter 20: “Margin of Safety” as the Central Concept - Graham’s fundamental investment principle
Chapter 1: Investment versus Speculation - Essential framework for your approach
Introduction and Commentary by Zweig - Contextualizes Graham for modern markets

Consider

Chapter 4: General Portfolio Policy: The Defensive Investor - Practical baseline strategy
Chapter 5: The Defensive Investor and Common Stocks - Selection criteria
Chapter 11: Security Analysis for the Lay Investor - Fundamental analysis basics
Chapter 14: Stock Selection for the Defensive Investor - Concrete screening approach

Least Important

Chapters 2–3: Inflation/bonds (dated specifics, though principles remain)
Chapters 6–7, 9–10, 12–13, 15–19: These dive into enterprise investor strategies, preferred stocks, convertibles, and detailed case studies—valuable if you go deeper, but not essential for core concepts

The 2003 edition’s Zweig commentaries after each chapter are worth skimming—they update Graham’s Depression-era examples with modern context.