If you're learning English in order to help advance yourself academically or professionally, use English in your classroom or workplace. In addition to easing the process of learning "jargon"-- words specific to a given industry or discipline -- regularly using English in a formal setting can help you become comfortable with speaking conventions used in more "official" environments. Even if your English is not formally assessed at school or work, you might find speaking properly to be more automatic if you practice in an environment in which high performance is the key to success.
As is the case with your native language, however, English is not all about business. Native English speakers use different words, phrases and intonation when not at work or school, so it's a good idea to make friends -- both native and non-native speakers -- with whom you can practice English in casual settings. This can be particularly effective if you incorporate English speaking into a hobby or activity you enjoy, whether you learn English words for your own knowledge or so that you can explain a custom or tradition from your country to someone unfamiliar with it who doesn't speak your native language.
Although spoken English is extremely important, English is also a "receptive" language. Therefore, it's important that your listening and reading skills are up to par with your ability to speak. In addition to conversations both within and outside of official situations, read English-language books and newspapers and listen to radio broadcasts and videos regularly. Expose yourself to English from all over the world. If you are living or working (or want to live and work) in the United States, for example, spend a few hours a week immersing yourself in British or Australian English. The more types of people you hear speaking English, the easier it will be for you to understand new people you meet. In addition to speaking, languages' other productive characteristic is writing. Bolster your English writing ability by communicating with friends and colleagues in written English in the form of emails, text messages or actual letters.