The very first inexpensive, easy and important upgrade for me was to change the spring weights.
A better hammer was the most significant for a clean break.
UPDATE: JMHO, The real story is that no one thing is best to see all the real improvements to make the 75 CZ a truly great SA/DA pistol:
If I were doing step by step upgrades maybe based on money outlay, this is what I'd recommend:
1. Polish everything (free or +cost of polishing materials), and install a Competition or Race hammer with the CGW floating trigger spring and adjustable sear to make it simple to DIY.
2. Install the old style 85 trigger and an extended firing pin, install lighter hammer and recoil spring (suited to the ammo you shoot "most often)
3. Install a short reset disconnector.
Leave the firing pin safety in place. With careful polishing and the above upgrades, removing this safety item gets insignificant improvements.
You decide what's most important to YOU with YOUR CZ