Practice speaking English wherever you can. Seriously. Take every tiny opportunity. If you live in an English speaking country then this is easier, but if not then you can talk to visitors. Don't be shy, and don't worry about making mistakes - just have a go! Even saying, "A cup of coffee to go, please," will help remove your nerves for when a true debate breaks out!
You can create opportunities, too! If you see someone you think speaks English that's taking a photo, ask them if they'd like you to take it for them. If you go to a restaurant that has an English menu, ask for it. It's these little things that truly set mediocre English speakers apart from the more natural ones!