When you want to be more assertive you need to respond in a thoughtful way.  Fairness should be your guide. Be direct, but be friendly.  Try to ask for what you need in a way that is clear, but not rude.

Speak up for yourself when someone is not treating you properly. But do it in a way that does not put him or her on the defensive. Tell the person how it makes you feel when he or she acts a certain way towards you. Your attitude will give the signal that you are not going to accept unfair treatment. It is also important for you to treat others fairly and kindly.