A particular favourite resource of mine, the Practice and Science of Drawing by Harold Speed, is a worthwhile acquisition for anyone interested in getting a solid foundation in representational drawing.
Drawing is the bedrock of all painting and I've been very careful to resist the urge to jump into painting at the expense of developing a solid grounding in drawing. My efforts in improving my drawing are ongoing but I've learnt a lot from Harold Speed
The Practice and Science of Drawing, first published in 1917, tackles the subject of drawing from two sides, first looking at line drawing and secondly at mass drawing. The section on mass drawing is most relevant to painters and, in fact, 'drawing' as Speed uses the term in this second section is, in effect, drawing with paint. This makes the exercises he suggests particularly relevant to me, in the sense that they consciously prepare the aspiring artist for work in oil at a later stage.
Aspiring artist, training in the classical tradition.