Most artists (and I am including in this all practitioners of the arts, e.g. painting, music, video art, installations, whatever) find the philosophy of art frustrating...partly because philosophers love to wallow in abstractions but also partly because they quickly discover that philosophers of art are more interested in saying something related to the main problems of philosophy than in trying to help artists. Actually I am not too sympathetic with artists on this point. It would be like philosophers being unhappy with painters because when they try to paint a philosopher they do not tell philosophers anything important about what it is to be a philosopher. However I do have something to say to artists about defining art which might be helpful to them anyway. Bear in mind, this is just my own view and may not be shared by any other philosophers.
Most artists will find the various definitions of art offered by philosophers and critics unsatisfying. However some will find at least one of these definitions to be at least somewhat close to his or her own definition of art. My point about defining art is basically this. It is a process that, despite the frustrations she might encounter when reading philosophy of art, is immensely valuable to the artist. Why? Because getting to know them, their advantages and disadvantages, can help the artist construct her own working definition of art. Why is this important? Well, as Socrates once said "the unexamined life is not worth living." By looking at the various dialogues of Plato, in which Socrates is usually the key character, the idea is that if you profess something (being a rhetor, a general, a politician, a friend, or an artist) then examining your own life is a matter of trying to understand what that thing is and what it takes to be a good example of that thing. Artists need to examine their own lives not just in the sense that they should examine who they are as individuals, but also, in the sense that they should try to figure out what an artist is, or who they are as an artist, or what "being an artist" should mean to them. Bear in mind that the first answer to this question is always going to be naive, shallow and relatively uninteresting. The point of the the Socratic dialogue is to show us that we need to test our definitions, discard the first rough attempts, and move on to ones that are more powerful, recognizing that we may (actually, will!) never get to a final one that is fully satisfactory. Unlike Plato, I do not believe that there is any eternal and unchanging answer to questions of this sort. (It is not entirely clear that Plato believed this either...but the orthodox view of Plato is that he believed final definitions were available at the end of inquiry.) Rather, it is important for each artist and each generation of artists to define art for herself and for themselves.
An example I often use is Robert Venturi and Denise Scott Brown. These are architects who came up with their own definition of architecture in the late 20th century. They claimed that a work of architecture is a decorated shed. Now, explaining their definition of architecture would require going into what they really meant by these two terms and how this was illuminated by their architectural practice and by the movement called postmodern architecture of which they were a part. The important point is that they realized that they had to come up with their own view of the essence of architecture, something that could be stated quickly in definitional form, in order to sum up the direction they were taking and the future they saw for themselves and for like-minded architects/designers. They took seriously the Socratic idea that the unexamined life is not worth living. They examined who they were. Moreover, the definition they came up with was immensely powerful. It summed up and also added momentum to a major movement in architecture. One could say, following a pragmatist conception of truth, that their definition was true relative to that moment in history. Of course there were many who disagreed, and in particular the deconstructivist architects who followed them made their own definitions of architecture (a strangely convoluted process since deconstructionists did not believe in essences or definitions...but so what! they still defined, and they still contributed to the changing essences of our culture). Part of defining something well is defining it in opposition to someone else's definition of the same thing.
When I have students from the arts in my Philosophy of Art class I encourage them to look at several of the great definitions of art in the past and to understand them as what Morris Weitz called "honorific definitions." They are not to be seen as science-like definitions: they are not much like the definition of "water" or the definition of "triangle." They are definitions that attempt to reveal, solidify and focus the essence of something that changes over time and that changes as the result of changes in the surrounding culture and as a result of debates and conflicts between cultural sub-groups, including, notably, generational sub-groups. To define art is to define art for your group and your generation for your time. So defining art cannot just be a personal thing. It has to do, and is closely related to, even larger definitional searches and even larger philosophical questions that are really as important to artists as to philosophers: questions like "what is the meaning of life?" "what is man?" "what is truth?" and even "what is real?" It also has to do with more politically and socially concrete definitional projects such as "what is it to be a Chicano" or "an American." To answer the question "what is art?" is to give at least a partial answer to these other even bigger questions. Socrates and Plato saw this. Moreover, these larger questions are questions that are of deep interest not just to you as an artist but to everyone else you know, even though not everyone takes a philosophical approach to these questions.
So, here is the big question: how do I become a better artist, or even, dare I say it, a great artist. I cannot base my answer on any empirical evidence. It is just based on what makes sense to me. In order to become a great artist one needs to ask the "what is art?" question in somewhat like the level of depth I have been suggesting here. You have to be asking the question with the view to the other big questions that it necessarily involves. That gives you (provides the foundation for) the 1% inspiration part of being "great," and the rest is the proverbial 99% sweat and just plain persistence/commitment needed to do well in any task. Greatness for an artist happens when you reveal/solidify, with mastery, the emerging essence of art as it relates to at least some of the fundamental questions of human existence. That's my hunch. And that is why I believe that asking the "what is art?" question in connection with the other even bigger questions is the most important question an artist can ask. This is not to say that the answer needs to be as articulate as that offered by Venturi and Brown in relation to their answer to the question "what is architecture." But you need to find some immensely powerful metaphor like theirs. Coming up with your own definition is coming up with your solution to life's problems as manifested in your art form and your art practices.
The biggest cop-out (and, I think, the path to the opposite to greatness) is to say "everyone has their own definition of art" and leave it at that. It is a deeply sad intellectual move since it cuts out all debate, all confrontation, all striving, and even, ironically, all self-examination. It is something Nietzsche's "last man" would say (and then he would blink -- see Thus Spoke Zarathustra). It is interesting that most people who say this do not yet have a definition of art of their own. They say it in order to avoid defining art, which is to say, in order to avoid the challenge of greatness. Finally, defining art can be something that happens in our art. When a great artist puts something forward and implicitly says "this, if anything, is art" he or she takes a stand about art itself (and maybe about life, meaning and humanity): this is the solution to the some of the biggest problems of my time up till now. This is my hat in the ring. Duchamp did this with Fountain. Rembrandt did it equally with The Night Watch. Joyce did it with Ulysses. Bourgeois did it with Spider. But other artists do it too in somewhat smaller ways: you do not have to be the greatest of the great to achieve greatness.