To remember the distinction between the two primary network theorems:
- Thevenin's Model: Voltage source ($V_{th}$) in Series with resistance ($R_{th}$).
- Norton's Model: Current source ($I_N$) in Parallel with resistance ($R_N$).
You can easily switch between them using a standard source transformation: $V_{th} = I_N \cdot R_{th}$ where $R_{th} = R_N$.