Reading is one of the most effective activities through which you can learn new words. However, do not just look through the written material, skipping unknown words, but underline every word you are not familiar with or whose meaning you don't remember, immediately looking up the definition of this word in a dictionary. Also, read material from different contexts, paying particular attention to the context in which you will use English. For example, if you are a medical doctor, read English language books on medicine.
Learning a word today doesn't mean you will still remember it tomorrow. Even a native English speaker may forget a certain word if she hasn't used it for a long time. Accordingly, repeat the words you've learned. An easy way for you to do this is to write down the words you've learned during the day in a notebook. Every day, repeat the words you have learned during the past month or so.
To learn a new word, think about the associations that come up in your mind when you think about it. For example, when you need to learn the word "globalization," you can think of the word "global" or the "globe." To learn the word "pineapple," think of the fruit that looks like a pine and an apple at the same time. You can also make connections by linking words that are the same or similar in your language and English. For instance, the English word "house" means the same as the German "Haus" and is also pronounced similarly.
Mnemonics assist your memory. Use them to help you memorize new words. For example, you can link the word "egregious" (outrageously bad) to the phrase " egg reach us," imagining we've made a mistake so bad that people are throwing rotten eggs at us and "egg reach us." This is not grammatically correct, but it's fun and can help you remember complex words.