Yo Kass answered
There are a number of ways you can improve your Korean vocabulary, ranging from spending some time on the internet through to spending some time in Korea.
The best way to improve your vocabulary in any language is by getting as much practice as possible. Learning Korean can be quite challenging,but luckily there are a number of mediums you can use to achieve your goal.
Watching Korean dramas to improve your vocabulary
In Asia (and increasingly the rest of the world) Korea is best known for a phenomenon known as Hallyu which translates to something like 'drama fever'. This term relates to the number of highly-addictive Korean dramas being produced in the country, and which end up being broadcast across the globe.
These Korean dramas are a lot like western 'soap operas', and are a great way to pick up on some Korean vocabulary in its natural context. Winter Sonata is one example of a Korean drama you may want to check out, and watching them with subtitles might help whilst you're still brushing up.
Get involved in your local Korean scene
It may sound obvious, but just hanging out with some Korean people is a great source of vocabulary. There may be Korean societies or sports groups in your area - alternatively you may even want to consider taking on a job at a local Korean restaurant. There are often many Korean students studying abroad, and I find that they're always more than happy to help someone looking to learn Korean.
Book your tickets to Korea
One final suggestion would be to save up some money and book a holiday out to Korea! Nothing beats getting stuck in, and visiting Korea will give you unique access to real-life situations like buying things in shops, ordering in restaurants and conversing with chatty taxi drivers- all of which will definitely boost your vocabulary!