Just to mention on the notion of these guides of what to say and what not to say...
I went along to my first GIC appointment not knowing what to expect. I was rushed and didn't have time for little more than a dab of foundation and a tiny touch of eyeliner. My hair was also styled poorly and my presentation was androgynous. I was also incredibly nervous and scared and babbled a lot. I think I opened with questioning whether or not I even had gender dysphoria and then just laid things out honestly - from childhood experiences to preferred pronouns (at that time it was anything but masculine) to how presenting in a more feminine manner made me feel. At the end of it all I was still pretty nervous and stupidly asked my practitioner for his opinion as to whether or not I had gender dysphoria. That was given as an affirmative with his suggestion that I had a transsexual but genderqueer / non-binary identity. At the time I hadn't even considered that and I am so glad that I was introduced to such concepts.
What was more interesting was that this seemed to break down some of his barriers to chatting in a more relaxed manner for the last 5 minutes or so of the appointment. After talking a little bit about identities I raised the question of how he could be so certain. At that point he made it very clear that he, and others providing such a service on the NHS, are aware of resources that inform people of the "correct" things to say to get onto hormones or access additional services (I've had no problems with this aside from waiting times). I can only infer from this that such standard responses are noted and probably adversely affect chances of getting treatment or taken seriously.
I think the best advice is simply to be yourself. Be honest. Even if that means digging up some painful and perhaps embarrassing memories. You also don't need to neatly fit into the typical ideal of a transwoman or transguy to get treatment on the NHS.
