Pretty sure that the title is straight forward but I'll elaborate. Over the years I've played guitar I have seen and heard many various claims that the way pick with your l hand (i.e your grip of the pick ), the way you fret the guitar or perhaps the way you mod or set up your guitar affects the tone tremendously.

To start the ball rolling I find that picking the string at a more or less 45 degree angle produces a rounder tone

What are the small things you do that improves your tone?
There's no real "best" tone and different things work better for different people.
But for me, for lower strings I hardly angle my pick at all and really push it down. Gives a harsh, metallic sound that I quite like. In general I like to hear a bit of string/pick noise coming out of my amp so I really hit the strings pretty hard, think slap bass. And I use a bit of legato on any notes that are meant to last a longish time, I find it helps with sustain and makes them sound a bit less one-dimensional.