Consume writing voraciously, and you will absorb writing skills by osmosis. You will come to appreciate an unexpected word or turn of phrase. You'll intuitively develop awareness of what makes a story arc engaging or a character tantalizing.
I'm not sure when the 'sympathetic character' became a necessity for modern authors. Certainly the Brontës didn't feel constantly pressured to write sympathetic characters, or they'd never have got away with Mr. Rochester