Here are some pointers on using body language to improve your effectiveness:
Eye contact. Practice using eye contact more intentionally to help you communicate better. Direct eye contact helps emphasize your most important word, phrase or sentence. But avoid staring and be sensitive to cross-cultural differences.
Physical emphasis. Other types of body language can also give extra emphasis to the main point of your message. For example, lean forward a little, especially when seated.
Conversational distance. Generally, the closer the distance, the tighter you want the relationship to be. The difference between talking across a desk and sitting next to a person is the difference between a supervisory speech and a friendly chat.