It's honestly not that hard if you put yourself in situations to be successful. I started in a high school GSA in my first year and never stopped partaking in such communities. I am in a hetero-relationship, am gender fluid, and find myself attracted to all numerous variations of people. Some days I feel more feminine and I do my best to rock it, others I feel masculine, and still some I'm somewhere else entirely. We all feel varying levels of what we consider appropriate as a man or woman or queer male or queer female and most simply don't know what to expect from any other form of person. The simple fact is that we feel a great many things and their associations to the gender binary are human created. We hide the feelings that don't match our identity and play up those that do. Once you find peace with all your feelings, you may find it much easier to to view others as simply being. 

That all said, I would just say the first step is changing your language. Yes what you think is extremely important, but your socialization will not change overnight. If you start using other language you will find that the assumptions interlaced with all the he's and she's can be far less illustrative of a person than what makes us define them as such. There is nothing wrong with speaking to a person as a he, she, or otherwise, so long as they identify that way and consent to it first.