Someone has caught up to me on the circuit, what should I do?
If you are being shown the blue flag, then you are not racing the car behind. To defend against them will only cost you both time, so instead the best move is to allow them through as soon as possible. To lose the least amount of time, move off the normal racing line on the next straight and lift off the throttle. Once the leader has passed you, get back up to racing speed and continue.
If there are no blue flags then the car is trying to take your current position off you. With a stern defence however, you will be able to keep a faster driver behind you without resorting to taking yourselves off the circuit.
Where are they most likely to attempt the overtaking move?
The easiest place for them to pass is on the straights, whilst utilising the slipstream effect. The best defence against this is to ensure you get a good smooth exit away from every corner. This will give you an extra car length or so to the car behind, reducing the amount of slipstream they benefit from. If done correctly, they will not be able to overtake on the straights and will instead have to pass you in the corners.
I am defending the straights, but they are very close in the braking zones and looking to pass in the corners. Where should I be placed for this?
To keep them behind, you will need to change your normal racing line. This will compromise your outright lap times, but will maintain your position for longer. As the car in front, you have the right to any line that you wish to take, and they must then position themselves either side of your car to complete the pass. This means that you have the advantage in defending as you have the first move, and can play your opponent when positioned accordingly.
As you approach the braking zone for the next corner, the best position for yourself is on the inside line. This will allow you to take the shortest route around the corner and forces your opponent to attempt a pass around the outside of the corner. It is much easier to counter an attempted overtake on the outside rather than the inside as you can run the car a little wider on the exit of the corner and pressure your opponent to lift and keep them behind you.