Learning anything new needs practice and perseverance.
To get a good command over spoken English, start reading English newspapers daily.
Read interesting and inspiring English novels and literature.
Speak in English regularly with people at home, office, society without feeling shy. You will make mistakes initially, but nobody is going to penalize you for that. Gradually, you will see improvement. Make English your primary language for communication.
Try to deliver PowerPoint presentations to your juniors or friends. That will help you to prepare the presentations in a well-crafted manner and then delivering that in English will slowly build up your confidence.
Watch English movies regularly to catch their vocabulary and sentence forming. But please stay away from learning slangs and abuses. Learn only good things.