Sometimes drawing lines on canvas to start a painting is useful, and sometimes they are a handicap. It’s one of those things where you need to experiment to see which method brings out the best in your painting. Beginners often assume that the more lines to start with the better, but that’s often not true. Too many lines can make for a tight (read: uptight) rendering rather than a free painterly expression. Granted, there are time I recommend lines. Certainly in portrait work, many artists start with a light pencil sketch on the canvas to help with accuracy. Difficult angles in architecture are helped by some lines as well. However, starting without line allows the painter to freely block in shapes and get an overall sense of composition and values more quickly. The best advice I can give is to start with as few lines as possible. And, if you like to start with a pre-coloured canvas that is medium to dark in value, white chalk is a great thing to draw the lines with.