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For JEE current electricity problems:

Simple circuits: Apply Ohm's law directly. Simplify series/parallel combinations step by step from the innermost group outward.

Complex circuits (multiple loops/batteries): Use Kirchhoff's laws. Assign current variables, write KCL at junctions and KVL around loops. Count equations = count unknowns.

Wheatstone bridge detection: Look for the pattern of four resistors in a diamond. If $P/Q = R/S$, the bridge arm carries zero current and can be ignored.

Meter bridge: $X = Rl/(100-l)$. For minimum error, choose $R$ so that $l \approx 50$ cm.

Potentiometer: $\varepsilon = kl$. For internal resistance: $r = R(l_1-l_2)/l_2$.

Power in bulbs: Find the rated resistance $R = V_{\text{rated}}^2/P_{\text{rated}}$ first, then analyze the circuit with those resistances. In series, the lower-wattage bulb (higher $R$) is brighter. In parallel, the higher-wattage bulb is brighter.

Common errors: (1) Forgetting internal resistance of the battery. (2) Using $P_{\text{rated}}$ directly in non-rated conditions. (3) Wrong KVL sign conventions. (4) Not converting units (mA to A, kohm to ohm). (5) Ignoring that galvanometers/ammeters have non-zero resistance.