The single biggest are intentional inclusion in more technical conversations and intentional non-inclusion in more self-appearance conversations. Along the same lines are expected background knowledge.
For reference, I'm in my mid-40's and transitioned over 5 years ago.
Prior to transitioning, I would frequently overhear or walk-into technical conversations about subjects that were relevant or of interest to me. While there were a handful of guys who understood my interest in technology and would intentionally include me, most simply wouldn't even think of including me (and I didn't know any women who were into technology). Thankfully, I never had a guy react badly when I included myself in a conversation, although I would occasionally get odd looks because of my interest and knowledge. Now I'm very intentionally sought out by colleagues (male and female) during technology conversations that are relevant or of interest.
Prior to transitioning, I frequently had acquaintances make suggestions about my appearance; make-ups I should try, how I should fix my hair, etc. While I've had lots of appearance-related conversations with my trans-friends, and I've had the typical, "wow you've changed a lot since I last saw you" conversations (but not as many as I expected). Other than those, I've only had one person comment on my appearance.
One of the more surprising topics that's changed has been car talk. I've never considered myself a car-person, prior to transition this wasn't ever a problem. Since I transitioned, it has come up with alarming frequency. While I've made a point of letting people know that I don't know a lot about cars, I still get comments that imply I'm an idiot for not knowing more.
Another thing that I find interesting is that prior to transitioning, I never had anyone suggest that I go a blind date with a friend of theirs; not one single time! Since I transitioned it's happened several times.