Budget for lights if you ride at night - one for the rear, one for the front, and if there are plenty of side roads and you are like me, one mounted in front facing backwards to illuminate you (on solid mode).

Learn proper riding technique in traffic. Learn hand signals. Use a rear view mirror if it helps. Be more careful of vehicles coming from side roads than from behind. Apparently the odds of getting hit from the side are higher than getting hit from behind.

Many cyclists stay nearer to the road edge at all times. I do not like this as some vehicles just overtake too close and then there is no room to adjust when that happens. So my personal technique is to occupy the middle of the lane until I see approaching traffic. Then I very deliberately move to the road edge in a gesture to give way. At the same time the traffic will have moved in the other direction to overtake. These simultaneous movements will have created a large enough gap for a safe overtake.

I do not believe a helmet is essential, but I do wear one. Be aware though that the helmet makes you subconsciously take on more risk than if you were helmetless.

A high-vis vest also helps.