In order to carry a pillion passenger on a motorcycle, a rider must hold one of the A category licences (A1, A2 &A). You cannot carry a pillion on just a CBT.
Once you hold the correct licence there are a few requirements you must comply to:
Ensure the motorbike is equipped with suitable supports rests for the pillion passengers feet
Ensure the pillion passenger is able to sit astride the motorcycle on securely fixed seat.
Ensure the pillion passenger is wearing suitable motorcycle helmet.
The motorcycle rider is legally responsible for ensuring that the passenger is safely supported.
There are no age restrictions for pillion passengers, but as a minimum they should be able to use the feet rests and supports.
Setting up the motorcycle
Before carrying a pillion passenger the motorcycle must be set up to handle the extra weight.
Adjust your rear shock absorber to compensate the extra weight
Adjust tyre pressures - generally they may need more pressure, but each bike is different so please do check your manual.
Check your headlight angle to ensure it is lowered to not dazzle other road users.
Adjust your mirrors. You may want to do this once your pillion passenger is onboard, so that you have clear vision.
Flip out pillion passenger foot rests, to ensure they are accessible.
Your pillion passenger may not have ridden a motorcycle before, and therefore, be unfamiliar with some of these key areas. Make sure these are discussed with your pillion passenger before setting off.
Mounting & dismounting
How to safely hold on and sit on the motorcycle rear seat
Communicating to each other
For communicating you may want to either agree a set of hand signals, or utilise Bluetooth communication headsets.
Riding style with a pillion
You may want to adjust your riding style when you first take a pillion passenger. The motorcycle will feel different and heavier.
You should aim to make all bike actions as smooth as possible.
Gear changing: during gear changing it is common to have a 'helmet bump'. This is where the pillion passenger leans forward as the momentum of the bike changes, and your helmets bump together. To reduce this, you should ensure your gear changes are smooth, and where possible quick, to ensure there is no loss of momentum.
Acceleration: with the extra weight your bike will accelerate slower than you are used to. Make sure you leave larger gaps when pulling out of junctions, or overtaking.
Braking: the extra weight will reduce your braking efficiency. Brake earlier than normal, but try and use engine braking as much as possible.
Steering: steering will be heavier and slower with a pillion passenger. Make sure you are looking ahead, and that you do not make sudden changes of direction that might unbalance the bike.
Once you have all of this, you are good to go.