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Letters To A Young Artist
The advice is essentially to get on with doing your art. Don't let the desire to look like at artist become more important that what you actually do. When you get an idea: carry it out. Don't decide that it has to be announced to the world first. Don't dwell on the problems you are having, and above all avoid associating with people who are persistently negative about things - those late night discussions putting the world to rights won't do your work any good.
Of course you shouldn't spend all your time on your art. The letters also recommend how you should spend the rest of your time. This was one point where I found the advice rather doubtful. There seemed to be lots of other things to do - morning writing, creative walks, maybe a part time job. I began to wonder whether there would be any time left - the odd quarter of an hour might be ok for an established artist, but I felt that one who was starting out would need to devote more time to their work.
But that's really a minor quibble, and I think that the book has some very useful advice, not just to those starting out as an artist, but also to anyone who needs to make time for what they wish to do.