When you finally make it into that sought-after prestigious gallery, you need to start keeping records of where your paintings are, the titles, when you took them in, when they were returned to you, whether they were framed or matted, the price you are asking, and hopefully, the fact that they were sold. Even if the gallery gives you a consignment sheet every time, it's better to have this information all in one place.
I keep a notebook with a photo of the painting (titles can be rather similar or repetitive) and a place for the information about its location. Here's a photo of one of the pages from my record book.