Answer: After some research , This is a list of assertive behaviours in different scenarios . I hope it helps  :)
Voice/Speech:
Firm
Warm
Well-paced
Non-accusatory
Face/Eyes :
Comfortable Direct eye contact
Firm but kind expression
Appropriate smiling
Body language :
Relaxed
Upright
Open
Calm hand gestures
Respect for personal space
Explanation:
In a meeting  :
Expresses their opinion Open body language
Speaks directly
General conversation:  
Makes eye contact with others
  Mirrors expressions
  Diffuses negativity
Achieving goals/objectives :
Takes pride in oneself and the team
Accountability
Takes accountability for own mistakes and others
    
 Project management
Usually reaches goals without alienating others
Management of others:
Makes sure everyone is on board with a decision