Decide what type of vocabulary might be most useful for you. There are words that appear quite often in every type of conversation, connected with every sphere of our lives. It would be beneficial to learn them, so you can be sure that even in the most stressful situation you will be able to use them effortlessly. It is also good to learn work-specific vocabulary, connected with your job. You will need to use such words on everyday basis and knowing them by heart will reduce the level of stress during your conversations with others.