Using Paint

Don't be miserly with your paint. Use it like it were dirt if you need to in order to accomplish what you have in mind when you paint. Not having enough paint on your palette will slow you down and hinder you immensly.

Direction toward Simplicity

I think one key reason that paintings are attractive lies in simplicity. It must be that way. It can't go the other direction and would be impossible to make a painting more complicated than nature with all its variations in texture, color, and ever changing light. Landscape painters recreate nature but must put it in simpler terms if by no other reason than only a few colors are used on a palette compared to the millions of nuances we see in life.
It could be that intuitively a viewer likes this simplification in his or her life as does the painter. It might make things clearer in some ways and gives answers to the heart and soul that might otherwise be lost in the ever changing three dimensions.
Art is a process of transition as light and paint are completely different from each other and can only be compared in the most general sense.

Using Photos

Painting from photographs, especially since digital photos can be viewed so clearly on a monitor, can have many advantages over painting landscapes in the field. The benefit is that your composition has been established and your borders defined. You can do all your composition in the viewfinder of your camera which eliminates one major step while painting. A two dimensional photo is also easier to grasp being that you don't have to transpose your three dimensional view in the open into two dimensions on your canvas.
There is no substitute for seeing though and everywhere you go, you must constantly analyze the things you eyes see in real life.
Use your own photos otherwise you will not have the same understanding about the subject even if seeing the real thing was only for a moment.

Watching

You can watch a violinist for twenty years but by doing so you won't be able to play a violin. Watching a painting demonstration won't teach you how to paint either. Don't kid yourself. Only picking up the bow or the brush can anyone become a musician or an artist. There is a place for seeing how things are done but too many people use it as a lazy substitute for doing it themselves and finding their own way. It satisfies a need, can give some motivation, but it won't really do much else. There is no substitute for doing.

Art School

People still ask me where I learned to paint and are looking for an answer about which school I attended as if the attendance at an art school had much to do with current paintings. I don't know why the notion that everything an artist knows came from a few years with a few teachers and the thousands and thousands of paintings I have created since then has nothing to do with that they are looking at in my studio presently.
Artists must give credit to themselves for creating art. This making of paintings has little to do with instruction and a whole lot to do with sitting in front of a canvas and finding ones own way with paint and brush.

Moving On

Don't labor over a painting. If it doesn't look right, try to figure out why and if it can't be fixed without excessive labor drop in and go on to another painting. Once your enthusiasm has been dampened it is difficult or impossible to regain it, so best move on. Your discouragement will be less than had you stubbornly stuck with a piece that just doesn't have a spark.

Tools

Never think that any tool you use is cheating. There is no substitute for knowing how to draw and one must know drawing, perspective, and such before it can possibly show in a painting, even abstract painting. Without knowing the basics even the most uneducated viewer will instinctively know something is wrong with the painting. But when an artist is firmly based in composition, drawing, and the use of line, using tools such as a projector, camera, or anything else for that matter to accomplish your goal can be useful and one should not be embarrassed by using those tools that are available to him or her.
I believe if the old masters had digital images available, they certainly would have put them to use.
When someone buys a painting from me they care very little about how the image was created. What they are buying is an image that speaks to them in some way. They don't care if I used a paint brush made of sable or one of old hemp. They are interested in the result, not the path that created it.

Preconcieved Notions

Get over the childhood notion that tree trunks are brown, the grass is green, and the sky is blue. Use your eyes and start to see the huge variety of color there is going on all around you and how they all interact to each other. Think about what colors you would mix on your palette to create that tree trunk you are looking at.

Self Consciousness

Don't be concerned about what someone else will think of you painting. Loose that self consciousnessabout it. The world is too busy with other things to really care anyway. If you paint what you feel and leave what you think other people will feel out of the equation , then your painting will be much improved not only in your eyes but in others as well.

Masses

Paintings must start out with a good foundation. In other words, large shapes have to be established before details are added. Otherwise the painting will collapse like trying to install door and windows before the walls are even up. One way to see these large important areas more clearly is by squinting the eyes as it will eliminates detail and bring masses into your realization more readily.
Of all the principles I try and follow when painting, laying in the large areas first is probably the most important to a successful result.

Color

Light leans towards color, not white.

Painting quickly

I try to complete a painting as fast as I can in order to keep the look of spontaneity that iniatiated the spark of enthusiasm I had to make the painting in the first place. A labored painting always lacks the excitement of the artist who created it and the viewer can consciously or unconsciously pick up on it right away.

Brushes

You can't do a good painting with a bad brush and it's a bad investment of your time and energy to think otherwise.

Courage

The most difficult part of painting is putting down the first brush stroke. It takes courage and a fearless committment.
The next most difficult part of painting is knowing when to stop.