As you read more! Especially the classics. They are bright, imaginative and very rich language. Among the "patriarchs" of Russian literature out of the competition by A. S. Pushkin – according to scientists-literary critics, he used about 16 thousand words. But conventional vocabulary, the "average" person is between 5 – 6 thousand. So, you should read Pushkin! The benefit of this is twofold: and join the beautiful, and remember new words.
Strain your own imagination! Remember that "under a lying stone water does not flow". Most try to find synonyms to the words that you meet or the nature of the work, or in everyday life. Got harmful, picky client? Immediately (mentally, of course) dubbed it "nerdy", "troublesome", "annoying", "annoying".
I saw the setting sun colored the horizon? Try to match as many definitions used to describe this sunset, "scarlet", "crimson", "begravelse", "dark pink", etc. Met on the street a pretty girl? Well, here it is necessary to be extremely insensitive subject, not to find lots of colorful, enthusiastic epithets!
You are going on a tourist trip abroad? There is nothing more natural, as to inquire about the country where you will visit. At the same time remember a lot of new words about its traditions, customs, and cooking. This can be very useful!
Or are you interested in any particular historical period? There could not do without memorizing many words describing the details of the costumes, weapons, social structure, relations between different social classes of the time. Let most of these words are obviously outdated, but your vocabulary they will still enrich.
Do not neglect even a purely scientific texts requiring expertise in a specific area. Still, at least some of the words to be understood and stored in the memory.
Try to write a story or a small story. It promotes not only the ability to Express their thoughts, but use as many words!