I have been around the art scene long enough to have been accepted and hung in juried exhibitions, local art club shows and library displays. I have won First Prizes, Honourable Mentions, and that great democratic award The Citizen's Choice. I have also had many of my submissions rejected with no explanation but most of the time with polite notes or phone calls thanking me for my interest and indicating my work did not fit the needs of the judging committee. The question beginners often ask is "What do the judges want?" What indeed.
If you've never entered any kind of art exhibit or contest, you might want to explore what type of exhibit you're thinking of entering. In my experience they usually break down into three main groups:
1) A national juried show
2) A local juried show
3) A local art club/library/community centre show1) A national juried show
These are usually truly juried shows. That means you submit one or more pieces, pay a nominal fee per entry, and send in slides or JPEG images to be judged and accepted or rejected. Most of the national shows requires slides as JPEG images can be modified and may not be an accurate reproduction of the painting itself. Once your submission/s have been accepted they are hung and judged by the same people who pre-selected you. Usually the judges do not know the artist's identity until the piece has been selected. By the time the show is opened to the public the winners have been selected and the appropriate ribbons displayed. If you enter in a national show the competition will be more intense as the pool of talent is greater and many professional artists will be competing for the honours. National show judges are usually highly respected members of the art world, and are chosen for their wide diversity of talents. If you even get a secondary award, as I once did, it's a great honour and good for your ego.
2) Local juried shows
This can get tricky. Some local art clubs may call it a "juried" show but in effect anyone can enter after paying a small fee. The number of entries is usually limited to two or three, and every entry is accepted and hung. Judging is then done by local judges who may or may not be truly impartial. There is nothing wrong with this of course, and for new members the honour of being hung in a public exhibition encourages further participation. Proud artists pose with their family in front of the paintings and they may even sell something. The standard of art exhibited is usually lower than national shows and professionals tend to avoid this type of exhibition. Often the most interesting result is to notice which painting receives the Citizen's Choice - it is rarely the same as the judges!
3) Local art club/library/community centre show
These vary widely of course, and attract strictly local artists who may be raising funds for local good works. Sometimes a judge is employed to select the winner and runners-up, but often the paintings/sculpture/pottery are there for sheer public pleasure. It's a feel-good exhibition and a nice way for any community to show how it cares for the arts. Some sales are often made and the small commissions go towards a good cause.
Before you enter
Before you enter a truly juried show you should try to find out who the judges are. Are they painters in watercolour? Oil or acrylic? Is their style realistic or do they do impressionism? If your work is highly realistic, as mine is, judges whose taste is towards looser styles will obviously pass you over unless the judging criteria has been set for them. To increase your chances of being selected, an unusual subject or a different slant on a familiar theme is often helpful. My painting "Running Colours" received the Studio Six Award at the 1996 Canadian Society of Painters in Watercolour juried show. I noticed many of the other winners had paintings with unusual titles and subject matter. Judges are only human after all, and if most of the submissions are standard flower paintings or country landscapes, they will tend to anything that breaks their monotony. I hasten to add there is nothing wrong with a beautiful flower painting or a majestic landscape, but judges look for innovation as well as technical skill.
I have never been asked to judge an exhibition so I can't give you the inside dope on what takes place, but I think judges should be given a set of criteria. The best I've seen so far is the information given on the Wet Canvas! site. Even if judges use only some of this criteria, judging would be improved over the hit and miss system in place much of the time.
You will have to decide what kind of competition you wish to enter, and starting at the local level may well satisfy your needs. As you move up to regional or national competitions the going will get tougher, but if it's your intention to make a living, or a part-time living, as a painter, you will gain better recognition by being in such shows.
If there are any judges reading this then my advice would be to study the link I've posted above. It will help make you a better judge and actually make your job a lot easier.
John Fisher