It is generally my favorite topic to teach. I cover both Organic Chemistry 1 and 2 for undergraduates. Understanding generally revolves around:
Spatial reasoning (e.g., Stereochemistry, Conformations, Syn/Anti relationships)
Conceptualizations of reagent types (e.g., Nucleophile/Electrophile, Strong/Weak Acids and Bases)
Developing reasonable and logical mechanisms (Curved arrow formalism, Lewis Structures/Formal Charges, Electron sources and sinks)
Proposing adequate synthetic schemes (Protecting Groups, Sequencing of Reactions, Functional Group Interconversion).
Understanding is significantly prioritized over memorization.