I used the tutorial by JuanHidalgo Miniatures on YouTube as a base and tailored it to fit my taste, definitely check his tutorial out - https://www.youtube.com/watch?v=JyNevDD-DpU

1. Prime the model white. I use Colour Forge Matt White spray.
2. Wash the whole model with a 1:1 mix of Vallejo Xpress Color Templar White (72.401) and Vallejo Xpress Color Xpress Medium (72.448). Tidy up any mistakes or overspill on the white areas at any step with with White Grey . Use this colour to edge highlight the white areas.
3. Paint the main body and any gun weapons with a 1:1:4 mix of Vallejo Xpress Color Deep Purple (72.409), Vallejo Xpress Color Gloomy Violet (72.410) and Vallejo Xpress Color Xpress Medium (72.448). Glaze in multiple layers from the tail toward the main body building up a smooth blend with the same mix until the colour at the base of the tail matches the body.
4. Add White Grey to the previous mix to highlight the weapon.
5. Basecoat all the chitin with a 1:1 mix of Tenebrous Grey and Strong Dark Blue .
6. Tidy up any overspill or mistakes on the arms with White Grey . Glaze the top of the arms with a 1:1 mix of Vallejo Xpress Color Space Grey (72.422) and Vallejo Xpress Color Xpress Medium (72.448), working towards the top of the arms to build up the colour in multiple layers.
7. Do the same but in a smaller area using a mix of 2:1:6 Vallejo Xpress Color Black Lotus (72.423), Vallejo Xpress Color Storm Blue (72.412) and Vallejo Xpress Color Xpress Medium (72.448). Build up a stronger darker colour towards the top of the arms.
8. Add a drop of Vallejo Xpress Color Gloomy Violet (72.410) into the previous mix for a final glaze towards the top of the arms.
9. Using a mix of 1:1:4 Vallejo Xpress Color Deep Purple (72.409), Vallejo Xpress Color Cardinal Purple (72.408) and Vallejo Xpress Color Xpress Medium (72.448) paint all the visible joints, fleshy bits, spiracles, tongues, tentacles, wings. Glaze this mix on the head working from the front to the back, building up a stronger colour towards the back of the head.
10. Glaze a 1:1 mix of Vallejo Xpress Color Deep Purple (72.409) and Vallejo Xpress Color Xpress Medium (72.448) towards the back of the head, on the edges of any wings and towards the tips of tentacles. Aim to have solid Deep Purple at the back of the head.
11. Use a 1:1 mix of Vallejo Xpress Color Black Lotus (72.423) and Vallejo Xpress Color Xpress Medium (72.448) glaze from roughly halfway towards the base on any claws, hooves and talons. Aim to have the base quite dark. Paint this mix inside the mouths and over the teeth.
12. Paint a mix of 1:1 mix of Vallejo Xpress Color Velvet Red (72.407) and Vallejo Xpress Color Xpress Medium (72.448) over any claws, hooves and talons.
13. Paint all eyes with a 1:1 mix of Vallejo Xpress Color Plasma Red (72.406) and Vallejo Xpress Color Imperial Yellow (72.403).
14. Black line the chitin with Black .
15. Highlight the chitin in broad lines with a 2:1 mix of Strong Dark Blue and Grey-Blue working from the centre to the edge.
16. Highlight the chitin with smaller, thinner lines of a mix of 1:1 Strong Dark Blue and Grey-Blue staying within the previously painted area.
17. Highlight the chitin again with smaller, thinner lines of a 2:1 mix of Grey-Blue and Strong Dark Blue staying within the previously painted area.
18. Add a final highlight of Grey-Blue with tiny lines and tippy tappy highlights on the edges.
19. Base the model however you see fit, paint the base rim with Black and you're done! I based mine with a plain and simple orange desert/wasteland base which I have done a separate tutorial for.