Hey there Thermo!
I don't have a painting guide per se but I did paint my first Rangers of the North a few months ago, I could probably quickly give you some basic instructions to get started on yours? Here's some pics of my first attempts:
And a quick run through of how I painted them:
Faces: Start off by covering the entire face with a dark flesh colour, I use Tallarn Flesh. Afterwards, use a flesh (or a light-brownish) wash to add depth. If you want, paint in the eyes (I use Bleached Bone with Shadow Grey for the pupils -> blue eyes) but be warned they require a steady hand and some practice! Then gradually add light highlights to the higher parts of the face with lighter flesh colour (i.e Dwarf - Elven Flesh). For exceptionally bright parts of the skin you can even mix some Bleached Bone and Elven Flesh together.
Hair: I basically use Scorched Brown as a base, then drybrush a Scorched Brown/Bestial Brown mix and add Bestial Brown highlights. For different hair colours, you could use a dark colour, then a mix of a dark and lighter colour, followed by pure lighter colour for highlights.
Cloak: Shadow Grey! This is an essential colour for the (aptly named) Grey Company in my opinion - other members might have other ways of doing their cloaks. Since painting these Rangers of the North I've made a bit of progress on cloak painting so I'll give you some general tips. Like the hair, use layering (Dark colour through to lighter colour), the deepest recesses of the cloak could be black (or a roughly 1-1 mix of Shadow Grey and Black). Start by covering the whole coat with the aforementioned 1-1 mix of Shadow Grey and Black. Then, with the next coat, use maybe a 3-1 mix of Shadow Grey and Black (or a darker grey instead of black -> experiment yourself and see what you like!) and only paint the waves of the cloak, i.e the 'parts that come towards you'. Finally, you'll want to add some highlights to the highest parts/the edges of the waves. To make this highlight look more natural, water the colour down a lot (here I used Codex Grey) and only put a bit on your Fine Detail Brush. Then drag it along the parts you wish to highlight -> the colour blends into the rest of the cloak, giving it a natural feel! This way of applying highlights could be used on other parts of the figs, too.
Leather armour: I used Dark Angels Green mixed with Codex Grey (I think it would've been a 2-1 mix -> try yourself) as the base colour and built up layers, gradually adding a bit more grey with each step. Try to keep the highlights green and not too grey though!
Chainmail: Drybrush Chainmail. Or Boltgun Metal if you prefer darker mail. If you find your mail to still be too dark -> use watered down black paint (or even better: black ink!)
Leggings: Codex grey layered up to Fortress Grey.
Boots, Belt and Armguards: Scorched Brown, covered with a black ink (or watered down black paint) add highlights with a lighter brown (Bestial Brown is a good candidate, Dark flesh could also be used -> experiment!)
Quiver and Bow/Spear:
Scorched Brown, heavy Bestial Brown highlights!
So that was just a basic guide (which turned out much longer than expected), hope it was of some use! My advice would be to really just try out yourself and don't be afraid of mixing colours, it opens so much more doors! Be creative!
Can't wait to see your Rangers!
Also: If you have Halbarad with Arwen Evenstar's Banner, then you can use these tips for him too, he's clad exactly the same as his Ranger bretheren. For the banner, use a black background with Chainmail, then Mithril Silver highlights, for the motive!