Read some critically acclaimed books. I'm currently reading "All the Light We Cannot See" by Anthony Doerr. He won the Pulitzer this year. Also, look into reading something like "The Elements of Style" by William Strunk. It has all the basics that all writers should know. Beware of the perceived 'advanceness' of the advanced section. Most of the post there are littered with pointless detail and the wrong usage of synonyms.