Every week, read a challenging book. History and biography, literary fiction, science, art, and music genres are a rich source of new words and phrases. Subscribe to good quality periodicals, such as National Geographic, The Economist, or The New Yorker.
Every time you come across an unfamiliar word, write it down in a notebook with its definition, pronunciation, a few synonyms, and an example of the word used in a sentence. Review your notes every week to commit new words to memory.
Join a book club meets either in person or online. You can pick up the speech patterns of smart people by conversing with them.
Listen to public addresses and read classic speeches from history. Important public figures and their speechwriters use language that is more elegant than what you hear in normal daily life.
Read and write letters to the editor of your newspaper. This is an exercise that will help you compose clear, concise, and logical arguments. Your letters may not get published, but imitation and practice will help you write more articulate and persuasive letters.
Brush up on the foreign languages you studied in high school or college. English has been heavily influenced by classic Latin and Greek, as well as by modern languages such as French, Spanish, and German.
Make a schedule to practice each day and sketch out lesson plans. Keep to your agenda and make monthly goals for yourself. This can be learning a certain number of new words, or finishing particular books. Discipline helps you learn more efficiently.