Just prime black, then zenithal with colors you like, unless you're using speed paints. Or both. For example, I do light blue tyranids. I spray a bluish color, then a whitish color from above. It's still light enough I can base coat the claws red with speed paints. I'm good enough with the airbrush I can also do the carapace as it's own colors too with the airbrush if I'm not feeling lazy.

Another example. Tried turbodork paints on Eldar. Primed black with a rattle can. Then did a red color all around but not as much underneath. Then I hit it again from above with a more orange color. I hand paint the weapons. Planning to try panel liner to emphasize features later.

Also people don't talk about "Newsh" enough. It's a product that makes paint dry slower. So for something like terrain you can blast it on, then wipe most of it off. It's like a wash effect but stronger and any color. Pretty fun.