Step 1) After putting together the model and priming it I always go over all my models with a watered down layer of black paint. This gives you a nicer surface to paint with and gives you complete coverage over the entire model. The first thing I did with this Genestealer is to do all the green fleshy bits that sit under the carapace. The reason for that is so you dont mess up the brown finish, and its really easy to paint around during the later stages as its the deepest part of the model. The flesh parts of this army are painted using Orchide Green, Knarloc Green and Scorpion Green.
Step 2) This steps is actually two steps combined. The first half is doing a quick dry brushing layer of Scorched Brown over the entire model, making sure you dont hit the green parts. The second half (which is what the picture is of) is done using Beastial Brown. This step instead of dry brushing I hand painted everything on, making sure to paint along the contours of the model, leaving small spaces between each stroke to start giving the appearence of a bone like carapace.
Step 3) I used Tallaran Flesh and painted over all the brown in the same style as the second half of step 2, except this time I put more distance between strokes.
Step 4) For the shoulders I did the exact same steps from 1-3 as the brown, except this time I used Liche Purple, A mixture of Liche Purple and Tenticle Pink (which sadly you cant get any more), then a mixture of Tenticle Pink and White.
Step 5) The final details were added. The black for the claws was finished using a mixture Chaos Black and Codex Grey (80-20), then straight highlights with Codex Grey then final Highlights with Fortress Grey. The Eyes are just yellow with small ticks of white paint for the teeth.
Step 6) The base. The ground on the base is Scorched Brown, the first highlight is Tausept Ochre and the final highlight is Bleached Bone. I find for basing its really important to use extreme highlights when doing the sand, since you want a huge amount of definition in what you are painting. If you used say Scorched Brown then Bestial Brown the contrast wouldnt be enough, and the definition of the sand would be lost. The ring around the base is Orchide Green.
The entire model was done with a #3 brush (so a very large brush) and it took about 1 1/2 - 2 hours total. I find that is one of the single most important things for painting models quickly is using a large brush. The second is setting up an easy to paint colour scheme. This army only has 4 colours total, all of which are easy to paint (brown, purple, green and black). Armies that are done with bright colours (ie yellow, orange and red) take way longer, as you need way more coats to get a solid colour. That being said the new GW foundation paint set helps out a lot on these colours. If you have any questions at all, please post and I will do my best to answer them :)