I thought that I was starting to get good at that. I felt like I was beginning to get used to (doing) that. It seemed to me that I was beginning to master that.

Hi, Harry, some ways to say "get the hang of that" [get / understand / comprehend / grok / own / pwn / rock] that [become / get] [well-versed / skilled / experienced] at that [become / get] [well-acquainted / familiarized / comfortable] with that [become / get] [used / accustomed / acclimated / adapted / adjusted / habituated] to that catch onto that pick up on that get that down get ahold of that pin that down put that in a headlock make that my b*tch learn the ropes of that hone my skills at that add that to my [repertoire / skill set] create a proficiency in that see that clearly get that into my noggin make an art of that make that second nature Okay, these are getting pretty tenuous... (By the way, I'm not saying you should say all these things, just that they might BE said. Some could obviously be rude.)