Most oil painters work on primed, stretched canvas. Pre-made canvases may be purchased at art supply stores and craft stores. Alternatively, some artists buy or make their own stretchers, stretch their own canvas, and prime the canvas with gesso.
If you stretch your own canvas, you will have an opportunity to prime the canvas to your own preferences. Some artists prefer to begin their paintings with a perfectly smooth surface. This may be achieved by priming the canvas with several thin layers of gesso. Once the gesso is completely dry, sand the canvas with fine sand paper to eliminate all texture.
The alternative to a completely smooth painting surface is a textured painting surface. The manner in which this is created depends entirely upon the painter's preferences. Texture comes by degrees of severity and is created with different tools for different effects. The most subtle and common example of textured gesso is created by the unsmoothed brush strokes that occur in the act of placing the gesso on the canvas. However, gesso may be applied to the canvas in nearly any way imaginable and texture usually arises naturally from the way that the gesso came to be applied to the canvas. For example, gesso may be applied to the canvas with the artist's own bare hands, resulting in hand prints or finger prints dotting the canvas surface.
Keep in mind that any texture--no matter how subtle--will be likely to show through the painting, unless the oil paint on top is applied very thickly. The texture should not compete with the painting itself, and it should work with the structure and design of the image, enhancing the painting.
Also keep in mind that priming the canvas is an absolute necessity. Although acrylic paint may be placed directly on raw canvas without negative results, oil paint will eventually degrade the canvas ,and so it must be applied to canvas that has been specially prepared with gesso.
Once the canvas is ready, set up your easel in a quiet room where you feel comfortable and can work without interruption. All jars of turpentine, palettes and tubes of paint should be ready and easy to reach. Any studies of the subject should be visible--either attached to the canvas or the easel, or on a nearby wall. Lay down any necessary tarps so that you need not worry about getting paint on the floor.
The most basic process of making any painting is as follows: apply paint to a surface. All else is a matter of preference. Have you chosen a subject? You don't have to. Painting by free-association, either creating a non-representational painting or just painting whatever random objects come to mind, is legitimate and can be rewarding. Most artists begin with an idea--this helps them as they pick colors and canvas dimensions--but it is not a prerequisite.
If you begin the painting with a subject in mind, you may wish to draw a sketch of the subject on the canvas. Oil paint will easily cover the drawing as it is applied to the canvas and you need not worry about the drawing showing through the final product. This will give you a basic plan to follow as you begin your painting.
Oil paints are nearly indistinguishable from acrylic paints after the painting is finished, but the two mediums handle very differently during the painting process. Acrylic is a fast drying water-based medium. Because of acrylic's fast drying time, the results are often bold and edgy compared to oil paint, which blends easily on the canvas. When you begin your painting, keep in mind that images painted with oil paints often have a dreamy, soft quality. To counter-act this (should that be your desire) try mixing the oil paints with medium. Medium can be purchased at arts and craft supply stores, and it is often used to thin oil paint. One of the side-effects of medium is that the paint seems to become smoother and clear-edged. Or, for an effect similar to water color, try thinning your paint with turpentine. The more turpentine in your oil paint, the more watery the paint will be.
Once the entire canvas is covered with the first layer of paint, you will probably have to step away from the piece and give it time to dry before you can lay down more paint. This is an excellent opportunity to reflect on the piece and consider next steps. Some artists like to turn the easel to face the wall, so the painting cannot be seen during this time.
You will have to wait several hours or perhaps even a day before you can proceed. Furthermore, you will likely find yourself setting the painting aside to dry more than one time before the painting is complete. Paintings often develop in stages, and oil paints in particular work this way since they are so slow drying. Every time you set aside the oil painting, you will give your mind a chance to consider next steps and how your painting is progressing.
Oil paint is an extremely slow-drying medium. Oil paint can take months and even years to completely settle, although most paintings will be functionally dry in a matter of days.
Some oil paints take longer to dry than others. In the process of making an oil painting, faster drying paints should be applied first and the slower drying paints should be applied second. This rule is known as "fat over lean". Oil-heavy paints (fat) take much longer to dry than paints that have been thinned with turpentine, or paints that have been made with a low oil content (lean). The result of painting lean over fat is cracking as the oil-heavy paints will constrict while they dry.
Remember that oil paint can only be thinned with turpentine, never water (it's an oil-and-water-not-mixing thing). Also remember that turpentine is a noxious and pungent substance that should only be handled in a well-ventilated room, or out-of-doors. Turpentine can also be used to get the clots of paint off your brushes when they need to be cleaned.