READING ! ... choose a good book and start reading it everyday, also you can watch english shows or movies to know a little bit the expressions and slangs they use... you have to make this a habit, everyday, whenever you have a spare time; there's no magic or an easy way, depends on you. You could write down the words you want to remember and do exercises using them in whole sentences. There are a million methods but just one "engine" : YOU ! ^^