Draw sketches. It’s the first and most important issue. Draw 5-6 sketches a day. You can do it anywhere – in the street, when you are at work or at home. It develops your style and accuracy of drawing. Also, it teaches you to be an observer and trains your memory.
Try to copy the old paintings. Surely it’s not so easy. And surely you won’t get a success at once. Be accurate and try to paint as close to the original as possible. But you should not only copy but study the story of the painter and his techniques together with the copy work.