I’ve playing tabletop games, rpgs and painting minis on and off for the past thirty years. I’ve always had nice’ish minis, but never really great - I still don’t get great, but they’ve improved a lot over the past few years, as I’ve started to pick up on a few mistakes.
#1 - thin your paints. Everyone says so, but once you start doing so, you stop getting that Brush texture, and you get so much better control of colours, as you get to control how much pigment actually goes on to the mini.
#2 - use a bigger brush! For years I used teensy, tiny brushes, ‘cause I was like painiting “minis”, right? But you gotta get some slobs of base colours on to that mini. Some shadow areas, some highlights etc., before you should move on to the nitty gritty details.
#3 - Shadows aren’t black. Indeed very little is - beyond black things - so you shouldn’t use black for shadows.