'be assertive about' is a correct and usable phrase in written English.
You can use it when you want to express the idea of standing up for yourself or your opinions and being firm and confident. For example, "You should be assertive about what you believe and don't be afraid to stand up for yourself."
But now is not the time to be assertive about your cleavage or (what remains of) your wealth.
Both the employed and the unemployed cannot be complacent about their skills, and must be assertive about keeping up with the latest computer languages and applications, she said.
And then you also have to be assertive about discriminatory things.
I think the key, as a woman leader, is to remember that what we do is going to influence others in the workplace, whether it be other women realizing that they can be assertive about their beliefs or men seeing another data point of a female colleague 'leaning-in'.
Furthermore, some studies have shown that non-smokers can be assertive about their right to clear air, providing social enforcement for these policies (Poland et al. 1999, 2000; Lazuras et al. 2012).
She envisaged that further difficulties might occur in relationships, e.g., when she took on greater responsibility at work, but that she now felt more able to be assertive about her own needs.
The Girl Scouts, meanwhile, have been assertive about their inclusiveness.
"He did not take well to that," he said, adding, "He was assertive about how wonderful he was".
Mrs. Sirleaf is assertive about why they rose in the government of the first woman democratically elected to lead an African state.
The White House says there is no reason for Mr. Bush to talk about recession absent concrete proof the nation is in one, and it has been assertive about pushing back.
But if there's a sexist tinge to viewers' dislike of certain female TV characters — amplified, in the case of Dana, by the fact that she's an adolescent female who is assertive about her opinions and her sexuality — I'd venture that there's a less sinister reason for the recent anti-Dana flare-up as well: regular old impatience with subplots.
