When I got my first handgun, a Remington R1 Enhanced, I didn't change a thing until I shot it a bunch. After that I changed:
Grips: installed a VZ ETC G10s
Trigger: Wilson Combat Ultralight Gold Cup Long Trigger
Magwell/Mainspring Housing: Wilson Combat bullet proof one piece magwell
Installing and fitting these pieces really helped me learn the platform. I feel far more prepared to deal with any future issues that may come up. More importantly though, my time shooting lots of rounds before making changes gave me direction on what I wanted to change.
Shoot it. Shoot more, then change one thing at a time until you're happy (spoiler: you'll never be happy!)