1. Current in series circuit remains same at all points in the circuit.
2. Voltage in series circuit divides between components
3. Voltage Divider formula could be used to find voltages on individual resistors in series circuit
V1 = R1 / (R1 + R2 +R3) * V_Applied
4. KVL is applicable
KVL : Sum of voltages in a close loop is equal to zero
5. Resistances in series circuit adds up directly
R_T = R1 + R2 + R3
Parallel Circuit Rules/Facts
1. Voltage in parallel circuit remains same on components connected in parallel
2. Current in parallel circuit divides among components
3. Resistor in parallel circuit adds reciprocally to give combination resistance
1/R_T = 1/ R1 + 1/R2 + 1/R3
R_T = (1/R1 + 1/R2 + 1/R3)^-1
4. Current Divider formula could be used to find current on individual resistances
I1 = R_T / R1 * I_T
5. KCL is applicable
KCL : Amount of current entering the node is equal to amount of current leaving the node.
For much better understanding you may watch this video given below.