How to Be Assertive in the Workplace
The best way to be assertive is to listen more than you speak. When you do speak, smile and be to the point. During office hours, avoid chit-chat, yet greet everyone you meet by name and in a statement. Don't just say "Hi." Use "Good morning," "Good afternoon," etc.
"Good morning, Tripti. How are you today?" "Good morning, Tripti. Hope you are enjoying your day," or "Good afternoon, Tripti. Have you had your lunch?"
A simple yes or no question is enough to let them know you are friendly but not necessarily their friend. When you greet someone by name, that person respects you for it. Later, you can add, "How is your son?" "How is your mother?" "How is your new accommodation?" etc.
Just in case they start to complain about something, give them an appointment to meet you in your office. Don't have any discussion outside your office. An appointment shows who is in charge, and since it's inside your den, you are the king/queen.
More importantly, practice your "Hello" smile in front of the mirror. It should be different from your natural smile—pleasant but professional.
All the best!