My suggestions, in no particular order:

• Front and rear lights, obviously. You can get lights that offer side visibility and get a front light with a cut off lens so you aren't blinding oncoming peoole.
• You can get vests or jackets that are basically one big reflector. The brand proviz makes a ton of options, but you can find them cheaper. I had one from a brand off Amazon and had peoole come up to me to ask about it because it was so visible.
• Ankle reflective bands are one of the best types of reflectors you can get.
• Tires with reflective sidewalls are awesome.
• If riding during dusk or dawn, wear high viz with reflective elements. High viz colours alone aren't very visible in the dark or by vehicle headlights at night.
• Ride in well lit areas, if possible.
• Ride slower than you would during the day.