Don't avoid negative folks. This may not appear assertive to you, but consider that it is setting a boundary.
Learn to say no. "No" is a frightening word for many women, but it is essential for assertiveness.
Embrace anger when appropriate. When men complain about not getting a date with them, many girls believe they did something wrong. I should know because I was one of them.
Realize you control your success and happiness. The issue with being a doormat and letting guys walk all over you is that we often feel compelled to save everyone as if we were a superhero.
Relationship "checkups" are important. I divide individuals into three categories during a health check: red, yellow, and green.
Know your non-negotiable boundaries. Everyone has certain things in a relationship that they simply cannot endure if they want to feel comfortable and happy.