Be confident about yourself. Confidence is really important for you if you want to be assertive. Assertiveness reflects confidence because when you get your point across and have others accept your advances, you actually reflect confidence in every possible way. If you are not sure about your capabilities and think that people may overcome your assertive behavior, you need to build up your confidence first and then impose your thoughts on others.
Never stop believing in yourself. Being assertive will require you to put trust in yourself. If you do not even trust yourself, people are not going to listen to you as they will see through your shallow assertiveness.
Make sure that the assertive communications you are using are actually working in your favor. When you try to become assertive, you actually use assertive communication. However, it is possible for an inexperienced person to resort to negative use of assertive communication. For instance, you might express arrogance in an attempt to get someone to do what you want them to do.
Be a good listener. People who are assertive for real are usually good listeners. You cannot drown out others just to make yourself feel good. You have to listen to what others think or say. When you listen to others, you get a chance to review your position as well because you never know what will happen next.
Make yourself better than others. No matter what field you work in, you have to make sure that you are better than others if you want to be assertive. Assertive people are mostly better than all those around them. Being better is not about being honest or humble, but it is about being more skilful. If you have more expertise than your peers, you can maintain the upper hand.