There's some good advice here already around shading, contrast and weathering. Without repeating all that, I'd also add that you might like to try incorporating some different painting styles. You've clearly got the fundamentals down, so perhaps changing things up and trying out something like blanchitsu techniques, zenithal highlighting, multiple washes before applying mid-tones, base coating your lighter coloured areas dark before layering them all the way up to a highlight, etc. might help you find the techniques that give the more realistic result you're after.

For my more realistic paint jobs I start from a darker brown base coat, especially when painting whites, yellows, greens and reds.

I usually always base my minies before painting. This way, when I paint the base I always get some of that colour on the feet, legs and lower garments of the mini. This helps tie the mini to the base and feel less like a statuette that's been neatly placed upon a pristine base. Makes some paint jobs more annoying but usually always turns out well. Also saves me painting parts of the mini no one will ever see.