Photocopy a page or an article and highlight all the words you do not understand. Look up those words and add them to your vocabulary diary.
When you come across a word you do not understand, first try to understand based on context.
Focus on prefixes and suffixes and find examples in a text you are reading. Underline and try to understand based on the prefixes or suffixes. Try to come up with the antonyms. These are words with an opposite meaning and are often related (unhappy - happy, misinformation - information, etc.)
Read a short story and try to retell or rewrite the story using as much vocabulary from the story as possible.
Note down nouns and adjectives you do not understand. Use a thesaurus to help you find synonyms to these words. Finding synonyms will help you learn groups of words with similar meanings.