The recipe I use for my DW infantry. Mostly using Citadel range paints.

1. Prime with Uniform Grey , Grey Seer , or Brush-On Primer . Black Templar is quite a strong color and takes well to light and dark greys.
2. Basecoat the entire miniature in Black Templar except the left arm or bare skin. Pouches, holsters, purity seals, and weapons can also be avoided. But it is optional. If you end up base coating them black it will not ruin the process.
3. Paint the eye lenses of the helmet Mephiston Red .
4. Paint the left arm Iron Hands Steel .
5. Paint the chest markings and Deathwatch icon with Retributor Armour . Alternatively, you can paint the chest markings Iron Hands Steel .
6. Paint the main areas of the weapon Iron Hands Steel , the rest Khorne Red , and any visible ammunition Balthasar Gold .
7. Paint the purity seal cloth with Rakarth Flesh and the wax with Khorne Red .
8. Paint any pouches or holsters with Mournfang Brown .
9. Shade any Iron Hands Steel with Nuln Oil . Shade the Rakarth Flesh , Khorne Red , and Mournfang Brown with Agrax Earthshade . Finally shade the Retributor Armour with Reikland Fleshshade .
10. If you want to follow my standard snowy base then first paint the flat areas of the base Fenrisian Grey and once that dries apply Valhallan Blizzard . Finish it off with a Dawnstone base rim.