Small yachts are almost invisible to shipping if there is a sea running, or visibility is obscured by haze or fog. When you add in the fact that your yacht is almost certainly lost in sea-clutter to the bigger guy’s radar, what can you do?
The first thing it to keep a good lookout, and assume that it’s up to you to spot them, because the odds are they are not going to see you.
Next, use your masthead running light. In the olden days, with incandescent bulbs, their power draw made this impractical. But with LED masthead bulbs so miserly on power, there is no reason not to be properly lit at night – with the most powerful masthead light you can find.
Last year we learned a new trick from our friends on Hawk. This is the use of 3M reflective tape (which we have applied to the forward "mast" and booms on WindHorse). If we were still sailing, we’d make sure the upper quarter of the mast was covered as well as using panels lower (topsides, bow, stern, and radar mast, for example). Not only will you show up better to other vessels, especially in fog, but your boat will stand out at anchor too.
White sails on a dark sea festooned with white caps do not stand out from the background. But colored upper panels, in particular "rescue orange" can significantly enhance your visibility.
Finally, here’s an idea from the world of mega-yachts. If you see them, but you are not sure they see you, turning on the deck lights can help. Even better would be a pair of spreader lights aimed upward on the sails. This makes them more visible to the other guys, and does less damage to your night vision.