A year ago I bought a second-hand tank, a thermometer and a bottle of developer, and started ruining film in the bathroom. It got better. These are the things that made the difference.
I spent weeks adjusting development times when the real problem was water that drifted three degrees during the run. A bowl of water at the right temperature for the tank to sit in fixed more negatives than any chart.
Four slow inversions every minute, the same way every time. Being consistent matters more than being clever.
Hang the film in the bathroom after a hot shower, when the steam has pulled the dust out of the air. Close the door and leave it alone.
Everything else, from the choice of developer to the brand of fixer, turned out to matter much less than I expected.