The American Psychological Association (APA) published its first guidelines for working with LGB clients in 2000. Since then the guideline has been updated and complemented with another guideline for psychological work with transgender and gender non-comforing clients. You can look for available translations into your native language, or you can use the original English version.
Both guidelines are accessible from the site of APA. The next excercise “Guidelines” details how you can go through the guidelines in a meaningful way.
American Psychological Association. (2015). Guidelines for psychological practice with transgender and gender nonconforming people. The American Psychologist, 70(9), 832–864. https://doi.org/10.1037/a0039906
Guidelines for psychological practice with lesbian, gay and bisexual clients. (n.d.). Https://Www.Apa.Org. Retrieved 1 December 2021, from https://www.apa.org/pi/lgbt/resources/guidelines