I think that looks really nice! You have a lovely subdued colour-scheme; the grey and the red works really well together.
Learning how to colour well is basically a mix of experimenting, learning colour-theory (which colours are complimentary, which colours clash, how to coloured lighting and shadows work) and getting comfortable with whatever software you're using. I think you're well on your way here!
I do my colouring in Manga Studio 5, but most of what it can do can be done in other software as well. The method I commonly use is to colour in the flat colours on one layer, and then do most of my shading on another layer on top of that, with the layer-mode set to "multiply" - this allows me to fudge around with the shadows and change where they are, and what colour they are, without disturbing the layer below. I also use "overlay"-layers to adjust the overall tone/atmosphere of the page, and do highlights - and sometimes I do really sharp highlights on a glow-dodge layer.
Don't be afraid to experiment with coloured light and coloured shadows! If the overall lighting of a page is yellowish (like streetlights at night, or a sunset), the shadows are going to be a bit purple, as yellow and purple are opposite each other on the traditional colour-wheel. Working with blues, greys and greens will result in a more subdued, moody atmosphere, while the yellows, reds and oranges result in a more warm and bright feel.
My one top-tip for colouring comics is to colour the backgrounds first. Colouring the backgrounds/environment first will make you think about lighting conditions and atmosphere and overall tone of the page - and let's be honest, most of us find drawing the characters more fun. If you put off colouring the characters to the last step, that means you won't get bored and wander away from a page before you've coloured the backgrounds properly.