read this article on Zenithal Highlighting first....
http://www.dakkadakka.com/wiki/en/Zenithal_Airbrushing%2C_OSL_and_Snow_and_Ice_Tutorial%2C_subject_-_Grey_Knight
I actually skip priming with my airbrush... I use a really dark color as a basecoat, then after finish painting the base coat + highlight layers, airbrush on a layer of matt or satin varnish to protect the undercoat The whole point of primer is to get the paint to stick better so its better protected, but
IMO if you use varnish after you finish the initial coating, its protected fine too.
So yea, base coat with like a 1-1 mix of dark brown and red, or scab red + black, or some kind of very deep red... then use a highlight layer of scab red initially, followed by progressivly lighter shades of red as outlined in that article I linked. You can use something like Vallejo Florescent Red for a final highlight on just the tips of the shoulder pads and helmet to get a finished look out of it.
Here's how I painted green blood angels with the technique I'm talking about here...
http://www.dakkadakka.com/dakkaforum/posts/list/418772.page
I know they are green, not red, but its the same technique with different colors, and it should look fine in the end.