Learn about realism using photographs (at least to start with).Any photograph is of something.Instead of selecting random subject matter select the kind you'd like to paint.An artist who lived in California wanted to learn how to paint polar bears.In addition his painting skills were quite modest.I suggested he do many small experimental studies by looking at photographs.It didn't matter if they're finished or not as they're ways of learning about bears.After 250 studies he did his first painting with no polar bear or photo.He was totally surprised at how well his polar bear turned out.Also the standard of the work was infinitely better than it had been in the past.He had internalized his learning.The polar bears he created were not any photographer's either.They were his!If you want to learn to paint animals, then choose animal photographs.Like the Californian artist don't select any animal focus on one (tiger, cat).Then even from the start you can become a specialist.You understand the animal and over time develop the paining skills needed.You will also know how to paint your subject your way.Eventually you can focus on another subject.If it is related to your original theme you will learn much quicker.For example one breed of dog to another or from one kind of animal to another.You'll note the similarities and also the differences.Progress from portraits to head and shoulders studies and then full figures.Follow this pattern for long enough, and you'll be able to paint anything!People who do anything well also do it faster than those who don't.That applies to painting like anything else, it's one of the indicators of skill.Skill in art, sport or even medicine is basically the same phenomenon.It's practiced behaviour in action.Most artists don't do anywhere near enough paintings to develop any real skill.Many small experiments will beat one or two major efforts every time.But you must do the 'hard yards'!Painting a large number of experiments develops skill, and also attitude.You'll become more discerning, because you acquire more experience.You'll not need, nor want, other people's assessments.Work on a number of experiments at the same to increase productivity.For you reduce wasted time.Once you run into a dead-end with a painting move to another for a fresh start.The initial painting is returned to with a different attitude, or set it aside again.Working on a number of paintings at the same time also saves materials.A particular colour can be applied to the work for which it was intended.BUT there will be other works where that same colour will be appropriate.When you buy paint, buy in quantity, but only use as needed.Can't remember what you did previously go with what you think of now.In the end it doesn't matter!Usually you'll find most works will finish fresh and roughly about the same time.But you can also learn by looking.That's how you learn about the appearance of things.Traditional art learning is based on looking and putting.It's possible to learn many simple things and gradually combine them.A problem is that you can only paint what you can see.But by actually painting such things you get to understand their appearance.You also develop skill at depicting those you do most.Let your experiments evolve.Those that don't work won't matter for you learn a great deal from the 'failures'.You'll learn what to do and what not to do next time.Regard these as exercises or studies or experiments.They are never going to be framed, sold or kept for posterity.Just do many and do them reasonably quickly.