Decide on a set number of words to learn in the next 30 days. Depending on how much time you are willing to devote to this project, two to eight words per day is an achievable goal. This will add 60 to 240 new words to your vocabulary.
Purchase a vocabulary book to select the words you would like to learn from. You want to choose words you will find useful, and a vocabulary book already presents a refined list of practical words, whereas a dictionary contains many obscure and trivial words.
Read over two to eight vocabulary words, their definitions, pronunciations and sample sentences every day. Reading the definition alone is not enough to internalize usage. Note that some words possess unusual spellings or require a particular preposition in sentences.
Create flashcards for your daily vocabulary words. On one side, write the word. On the other side paraphrase the definition in your own words, use the word in one or two of your own sentences, and come up with a synonym and antonym for the word. Also include the word's part of speech (noun, verb or adjective, for example).
Practice your flashcards everyday until you have the definitions memorized. Review previous words everyday as well; don't put words aside in case you forget them. At the end of the 30 days, test yourself for all vocabulary words. Discard those you know and review those you still struggle with.