assertive...a new vocab in my life

In my work Life,
i was learning to say NO in my way that when i feel that is what i should say.

now....i m good in saying NO

One teacher colleague of mine advised me that i should be

"ASSERTIVE"

describes someone who behaves confidently and is not frightened to say what they want or believe:
If you really want the promotion, you'll have to be more assertive.

YA....dis is the word keeps running about in my mind.