I've had a funny relationship with allies in the sense that I for years have pretended to be one (straight and cisgender), and the vast majority of people still think I am one. I learned to be very submissive regarding any interaction with LGBT folk because of this. I don't dispute anything they say even if I feel they are gravely wrong because I would become that opinionated ally that oversteps boundaries. I often feel more like a servant than a person.
For some strange reason, I have seen allies do more the LGBT community in the place I grew up than LGBT folk themselves. Maybe it was because since I was an "ally," I was outside the LGBT and thus had know idea what they were doing. Maybe it was because LGBT members of our advocate group never really talked about how they were LGBT, and thus assimilated into the straight, cisgender erasure. In the place I live now, the LGBT is much more open and active but that does change the fact I'm outside their community, and thus can't really have an equal, meaningful relationship with it.
To add to the backwardness of my experiences, the people most opinionated about what is and is not trans are trans folk themselves. I don't blame them; they have to deal with stigma and misinformation everyday. The problem with how some of them do it is that it creates a group of outcasts amoungst outcasts, and I am most definitely one of them. All and all, my unusual experiences had lead me to believe that the best way to support trans folk is to stay an ally, even if that meant they can never fully relate to me or trust me.