To improve your vocabulary you have to do the same thing that you do to become friends with people. If you meet a person in a party and never see that person for a year, you are eventually going to forget the person. But if you meet that person frequently, you will remember the person's name and remember about the person's life. The person is then no longer a stranger and is a friend now. The same concept applies to words. You have to encounter the words again and again. You have to bump into each other frequently. When you see the same word in several books or movies or in news, the neural connections in your brain fires up. Due to this, the brain creates more and more connections which helps in remembering and recollecting the word easily.
Start going through the following word lists leisurely. Relax and don't get disheartened by the massive number of words in English.
vocabulary.com - They have a section in bottom right corner which shows the occurrences of that word in media like The New York Times and The Washington Post.
There are always two steps in learning vocabulary.
Knowing the meaning of the word.
Knowing how to use the word in a sentence.
So that's how you improve your verbal skills. The key is to:
Use as many sources as possible to get different perspectives. (It's like meeting the friend in different outfits at different places and events.)
Encounter the words frequently. (As you make many more friends you will forget your older friends. So meet them again.)
The best way to improve your language skills is by speaking the language. There is no substitute for practicing with real people. For people who do not have anyone in their vicinity to practice their speaking, I have made the website SpeakAlley.com to help people speak online with other learners. I have started adding English vocabulary to the website to help learners improve their vocabulary.
Going through a list of vocabulary is of no help. Try to incorporate the words in your daily conversation. The answers to the following questions will also help to speak with confidence.