How to be more assertive?

I work as a CNA and I work under supervision of RN's and BSN's. I know they kinda tell me what to do, but is there a way to be assertive than to take the load of everyone's work? I don't want to be manipulated, or taken advantage of. One nurse said I was agreeable, and I don't want to be like that. I am short and innocent looking too, so people always think I am younger than I am. I want to be strong and confident. Or should I just go to work do my job and go home? And if anyone gives me trouble just stick up for myself?

How to be more assertive?
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