Is it necessary to plan a painting in careful detail before you start, or should you let it evolve as you go along? Planning a painting can be a help as you know exactly what you're going to do, but it could also inhibit spontaneity. Letting a painting evolve as you work is very free and lets you be spontaneous, but also leaves you open to the possibility that the painting won't go anywhere and you'll end up with a mess.
Ultimately the degree to which you plan out a painting depends on your personality, some people find it essential and others a hindrance. But regardless of how detailed you like to plan (or not), there are several decisions that have to be made before you to start to paint.
1. Decide On a Subject
Deciding on a subject is the logical first step as it influences the format of the support, the type of support used, and the technique you're going to use to create the painting. If you've only a vague idea of what to do with an appealing subject, such as a glorious landscape, sketching or doing small studies rather than a full painting will enable you to see whether the composition and selection of elements works well without wasting time or materials. A pleasing study can then be used as the basis or reference for a full-scale painting.
But if you find that doing a study makes you stiffen up when you come to do the large-scale painting because you're focusing on replicating it, rather than it reminding you sufficiently of the original scene, consider doing only quick sketches to see if a composition works and taking reference photos to work from back in your studio.
2. Decide On the Format
Having decided on a subject, you need to decide what the best format for the support is, whether it should be landscape or portrait, or perhaps square. What shape of the canvas will best suit the subject matter? For example, a very long and thin canvas used in adds a sense of drama to a landscape, especially one of a wide-open space.
3. Decide On the Size
The size the support will be should also be a conscious decision. A painting shouldn't be a particular size simply because that's the size of the sheet of paper you have. If you buy primed and stretched canvases, have several in various sizes to hand so you've a choice. Think about how the subject would look if it were painted small, or perhaps very large. Are you going to work lifesize or oversized? For example, portraits which are oversized are very dramatic.
4. Decide On a Medium and Technique
If you only ever use one medium then you don't have to decide which one you think is best for this particular subject. But what about the technique you're going to use? For example, if you use acrylics, are you going to use them thickly or thinly, like watercolors, are you going to use retarders to slow down the drying time? If you use watercolors, are you going to use masking fluid to keep areas white?
5. Decide On the Type of Support
Are you going to paint on canvas, primed hardboard, or paper? Will it be a canvas with a fine weave, such as linen, or a coarse weave that will show through? Will it be a smooth, hot-pressed paper or a rougher watercolor paper? This is a decision that not only influences the texture of the final work, but also how you work, for example canvas will stand heavy impasto being reworked repeatedly. Alternately, the technique you're wishing to use will determine the best support.
If you are using oils, acrylics, or gouache, will you be using a ground and what color should it be? How about using a complementary colour to the main colour in the picture? If you are using pastels, what colour paper will you use? And will you lay down an initial layer of complementary colors?
6. Decide On Colors
Are you going to use color realistically or not? Are you going to use whatever colors you've got or select out a few to make up a palette just for that painting? Working with a limited range of colors can contribute to a sense of unity in a painting and great a sense of identify or unity between paintings.