Record the complaint in the customer's words
"Noise from front left when braking" is more useful than "brakes". The original words let the technician reproduce the problem and protect you later if the customer says the fault was something else.
Capture the vehicle's condition at arrival
Odometer, fuel level, visible damage and items left in the car. Two minutes here prevents most handover disputes.
Separate diagnosis from approved work
Keep what was found apart from what the customer agreed to pay for. Additional work should go through a new estimate or approval, not a verbal promise at the counter.
Close the card with what was actually done
The final job card should list the labour performed and parts fitted. That list is what the invoice should come from.