Obviously to be seen equipment would be lights and reflectors. I don't put a whole lot of faith in reflectors though I do use them when I ride at night as an added benefit.
As far as lights go I usually use two tail lights, one of the seat tube and one on the helmet but I broke the helmet one a couple of days ago so I need another. My main tail light is a Light & Motion Vis 180 that puts out 70 Lumens, I'm probably going to buy a Lezyne Zecto Max Drive Rear 250, it seems to be the best deal for the lumens output, then the Lezyne will become my main light and the L & M will be my helmet light. How I use these is a bit weird but there a reason for my insanity. I run the main light during the day on flash to attract attention, and the other is off; but at night I run the main light on steady mode and the helmet one is flashing. So why do I use one on steady and the other flashing at night? Because studies in Europe have shown that a steady light enable motorists to ascertain how far away they are from the light source more accurately so in Europe you can't even buy a flashing rear light; but studies in Canada have shown that a flashing light is better! So I simply combine the two studies!
I also use two headlights, the main and brightest one is on the bar, it's a Philips Saferide, and the other is on the helmet, it's a Cygolite 480 OSP. I do not use head lights during the day unless it's raining then I use the Cygolite because it has a flash mode that the other one does not. Even though that Philips is now considered old it's still the brightest on the road when I see others at night due to the aimed optics. Too bad Philips decided to stop making it because it was a very well made and bright light.
The only other thing I add when riding at night is a neon green mesh vest with wide reflective bands running across it. I got mine for cheap from Home Depot for $12. It looks really nerdy so if looks is important to you well you may want to skip this vest, but I think since workers use these things at night it must have some value to it. Other reflectors I have simply come with the seat bag, the shoes, the jacket etc, I don't buy anything to specifically add to reflectively other than the vest.
I'm not saying I have the best lighting, I'm sure if I was to spend a great deal more I could get better lighting but what I do have I like, and in fact where I live it's difficult to find anyone even using lights front or rear, so I'm the odd duck!
Improvement wise, the only thing I use to do which I don't do anymore simply because I'm down to one and hopefully two tail lights, but I liked the idea, was that I use to have a tail light on each rear seat stay PLUS one on my helmet, at night this formed sort of a triangle, I just don't know how effective that was vs just two in row.
I haven't had any lighting difficulties.
What I would like to add is I use rechargeable battery systems of course. Modern batteries are not as good as the older NiCad's but they are smaller, the problem with the new [censored] is that the battery themselves won't recharge as many times as the NiCads did, NiCads could be recharged from dead to full at least a 1000 times, the new stuff you MUST charge after every use no matter how little you used it, if you completely drain the new bats you will dramatically shorten it's ability to charge over and over. The new bats are only capable of lasting about 3 years to 4 years, it may be the quality of the battery being used by light manufactures or it could just simply be that the small ones just don't last. I know that Shimano says that their battery for their electric derailleur system will only last 2 years on average, which for the price of that battery I think it's rather stupid, I also think it's stupid that we pay $50 some odd dollars for a light and that battery is not replaceable so you throw it away and get another. For some reason the Cygolite that I have is going on 6 or 7 years and the battery is still good, but it may be using a different chemical makeup the the newer stuff, but my L & M is not lasting as long as it use to on run time and it's 2 to 3 years old. The Philips is 5 to 6 years old but it uses rechargeable AA NiMhs batteries, which I had to replace the original ones earlier this year because they wouldn't hold a charge for more than 15 minutes on high. So anyway, if you want your batteries to last you have to keep them fully charged after every use, and you cannot store them in temps below 36 degrees or above 90 degrees, and never let them stand around in direct sunlight. You also need to make sure the battery is cool before you recharge them, and make sure they cooled down after charging before you use them. I practiced this stuff so maybe that's why all mine stuff is lasting a year or two longer than average. Anyway in my opinion these new batteries suck.