Ride to see and be seen. High-viz ensures you contrast with the dull background of gloomy days and general greyness of streets - and are seen. Legally, lights are required in the hours of darkness and can help ensure you are seen on dull days.
Do not get distracted with headphones or smartphones - you need to hear and see all around you, any distraction gives you less time to react to others on the roads.
Ideally, ride about a third of the way out from the pavement (1 metre or so) so you can be seen better at junctions and are out of drains, gutters and debris. Wear high visibility items and lights at night to be seen. High-vis stickers on your helmet are effective. A helmet is recommended - it is a legal requirement in some countries for good reason, but not in ours.
Pedestrians, particularly vulnerable elderly or disabled people, can feel threatened by bikes on pavements. As well as riding on the pavement being illegal, when you come off the pavement into the road, you may not be seen by other road users. Cycling off the pavement may cause traffic to swerve into others - or hit you.
Be a door's width from parked cars as you pass them - in case the door suddenly opens. They may not see you.
Obey traffic signals and signs - they are there for all road users. Going through a red light could mean colliding with a vehicle not expecting you to be there. More local information can be found here.