One of the most effective ways of keeping safe on a bicycle is to make sure that you are seen! This can be accomplished in various ways.
Most obvious is to wear bright coloured clothing or a reflective vest. At night front and rear lights must be used. Even during daylight hours using some of the bright flashing LED lights can help in separating you from the background visual clutter that a motorist is dealing with. Making yourself stand out from the rest of the scenery helps to put you on a motorists “radar screen” a lot sooner, therefore helping them adjust their speed and path to minimize any conflict.
Statistics show that most accidents involving a motor vehicle and a bike are not where the cyclist is hit from behind, but frontal and side collisions. Hence the importance of a front light, even during daylight hours. (Use a bright light in flashing mode)
You don't have to buy the latest in bright lycra cycling garb to make yourself visible, or wear an ugly bright neon green jacket like I often wear. (Hey, I got a good deal on it and people do notice me!) Wear comfortable, normal clothes and use bright fashion accessories like scarves, backpacks, fanny bags, helmets or just throw on a reflective vest.