firstly, we should aducate ourself about transgender issues.
Second, we should be aware of our attitudes concerning people with gender-atypical appearance or behaviour.
Third, we need to use names or pronouns that are appropriate to the person's gender presentation and identity; if in doubt, ask their preference.
Four, do not make assumptions about transgender people's sexual orientation, desire for surgical or hormonal treatment, or other aspects of their identity or transition plans. if we have a reason to need to know, just ask them nicely.
Next is, do not confuse gender dysphoria with gender expression: Gender-dysphoric males may not always appear stereotypically feminine, and not all gender-variant men are gender-dysphoric; gender-dysphoric females may not always appear stereotypically masculine, and not all gender-variant women are gender-dysphoric.
Then, we need to keep lines of communication open with the transgender person in our life.
Next, get support in processing our own reactions. it can take some time to adjust to seeing someone who is transitioning in a new way. having someone close to us transition will be an adjustment and can be challenging, especially for partners, parents, and children.
Last but not least, transgender people need to seek support in dealing with their feelings. Mental health professionals and support groups for family, friends, and significant others of transgender people can be useful resources.