First, practice your listening and comprehension skills. Conversation can only occur if you understand the other person and can respond to what they are saying to you.
Next, practice asking good questions and responding to specific points someone tells you. For example, if you meet a new coworker who says "I work in the accounting department, I've been here for 5 years" Ask them about their experiences in the last five years. Or ask them how the company has changed and if they still like working there.
Also, don't say no to any opportunity. Any chance you have to communicate in English, take it! Don't be afraid of not speaking perfectly. It's a process and people will understand that.
Keep speaking, keep interacting and you will improve. If you would like to discuss business communication, please feel welcome to ask me any more questions!