Discrimination based on gender identity- including other's perceptions of a person's gender identity- and gender expression affects both trans- and cisgendered people. No matter who it's aimed at- from the person who's denied a job because the name and sex on their ID doesn't match their appearance, to the child who's subject to bullying because they're too "girly" or because they're a "tomboy"- discrimination based on gender identity or expression can have devastating effects.

So, what can you do about it?

Individually: Examine your own actions and speech. Do you use the correct pronouns when refering to transpeople? If someone corrects your pronoun use, do you use the pronoun they ask you to? Do you treat masculine men and feminine women with more respect than you would feminine men and masculine women?

Locally: Support local laws to prevent discrimination based on gender identity, expression, or presentation. If you see someone discriminate against someone because they are trans or gender non-conforming, don't ignore it-- call them on it. Write letters to local newspapers or other media sources. Check your employer's anti-discrimination policy to see if it includes gender identity/expression, and, if it doesn't, suggest that it be added.

Nationally: Support laws to prevent discrimination based on gender identity, presentation, or expression. Buy from trans-friendly companies. Support political candidates which support anti-discrimination legislation.