When speaking English you should be confident and speak as often

as possible to as many people as you possibly can! At home, at work, on the bus/subway and at your school or work place. Do not be shy about making mistakes! We learn from our mistakes.
The more you practice the better and more confident you will become in your pronunciation and your vocabulary.
Remember, learning English is a skill like learning to play a new instrument or a new sport – the only way you can improve is to actually do it!
Practice Makes Progress!