You should also be selling at least half of everything that you produce within a six month time period. As with any other price-setting circumstances, be able to justify all increases with facts. Never raise prices based on whimsy, personal feelings, or because you feel that they've remained the same for long enough. Remember that today's collectors are more sophisticated than ever. The idea of falling in love with one piece of art and having to have it at any cost fell by the wayside years ago.
Collectors now research and compare before they buy.
The only ones who don't are new to the game. Just in case you get lucky and find one who's a little naive, by the way, resist the temptation to take advantage and overcharge. You risk the possibility of turning them off to continued collecting. We all know that we need all the art collectors we can get. Lastly, have something for everyone.