The wider the vocabulary you have at your disposal, the easier it is to speak a language fluently. Familiarize yourself with as many simple, everyday Korean words as possible - you'll be surprised at how quickly they build up!
When you hear a word in English, think about how you would say it in Korean. If you don't know what it is, jot it down and look it up later. It's handy to keep a little notebook on you at all times for this purpose.
Attach little Korean labels to items around your house, such as the mirror, the coffee table and the sugar bowl. You'll see the words so often that you'll learn them without realizing it!
It is important to learn a word or phrase from ‘Korean to English’ as well as ‘English to Korean.’ That way you will remember how to say it, not just recognize it when you hear it.