What are the three rules of oil painting?

Some tips for starting out:

• Make sure that you always have two containers of solvents prepared for oil painting and keep them separate. One of these should be for cleaning your brushes and one for thinning the paint. Distilled Turpentine is best for thinning and White Spirit is best for cleaning. Low-odour solvent equivalents such as Winsor and Newton’s Sansador offer a flexible alternative and can be used for either purpose.
• It is worth collecting old rags to be used for wiping brushes when you clean them. 
• There are three rules to follow when painting in oils because colours dry at different rates: ‘fat over lean’, ‘slow over fast’ and ‘thick over thin’. (1) Fat over lean: when painting in layers, each successive layer must be more flexible than the one underneath. This rule is maintained by adding more medium to each successive layer. (2) Thick over thin: thick layers of oil colour are best applied over thin under layers. Thin layers on impasto paintings are likely to crack. (3) Slow vs. fast drying colour: slow drying colours should not form continuous under layers as any faster drying layers on top may crack.
• Painting in oils means that you need to prime the surface first, whether you are working on paper, canvas or board. If you don’t, the oil colour will bleed into the support and eat away at its structure over time. You can either use an acrylic-based primer such as gesso for this or an oil-based primer. Winsor & Newton also has an extensive range of gesso-primed canvases, paper pads and canvas boards for oil painting that allows you to start painting right away.
• Artists tend to use hog hair brushes when working in oils because the paint is thicker. However, it is always worth having a range of brushes, including finer and older misshapen ones (synthetic or natural-haired), which allow for detail work and the creation of different textures.
• It is worth investing in good quality materials. Having the right materials and tools means that you will achieve much better results.