I'm gay and been to counseling. The big one I can think of is just reassuring clients that you're an ally. That may depend where you practice, but it really matters in conservative areas like mine where that can't just be assumed.
And I've also had a couple counselors who seemed really fixated on heteronormative/cisnormative gender roles, so probably avoid that (although the fact that you made this post leads me to believe you already know this)