For all Tau infantry from the Kel'shan sept - Fire Warriors and Pathfinders. Should also work for drones, and for Battlesuits with a couple tweaks.
Yes, this is definitely far too detailed for basic infantry, but I figured I'd go to town!

As a note here, I painted the entire mini as subassemblies (head, torso, legs; arms separate, backpack and shoulder guard separate). This isn't necessary, but I was able to get to a lot more of the details.

Undercoat with Mechanicus Standard Grey

Fatigues

1. Base with Corvus Black
2. Chunky highlight with Eshin Grey
3. Wash with Nuln Oil (or Agrax Earthshade for a 'dirtier' look)
4. Highlight again with Eshin Grey
5. Fine highlight with Dawnstone

Light Grey Armour

1. Touch up undercoated areas with Mechanicus Standard Grey
2. Base with Dawnstone
3. Shade recesses with a mix of Mechanicus Standard Grey / Contrast Medium , aiming for areas that would be shadowed (sides of chest panel, underside of helmet etc)
4. Shade armour panel lines with Nuln Oil
5. Touch up panel edges with Dawnstone
6. Highlight with Administratum Grey
7. Fine highlight with Celestra Grey

Dark Grey Armour

1. Base with Eshin Grey
2. Shade armour panel lines with Nuln Oil
3. Touch up panel edges with Eshin Grey
4. Highlight with Mechanicus Standard Grey
5. Fine highlight with Dawnstone

Yellow Armour (sept colour)

Note: Steps 3 to 5 can be skipped for any smaller pieces of armour.

1. Base with Averland Sunset
2. Layer with Yriel Yellow
3. Recess shade with a mix of Averland Sunset / Yriel Yellow / Contrast Medium
4. Shade panel lines with Agrax Earthshade
5. Highlight with Yriel Yellow
6. Fine highlight with a mix of Yriel Yellow / Screaming Skull

Shoulder Icons

1. Shade the T'au symbol with either a mix of Averland Sunset / Yriel Yellow / Contrast Medium (for the shas'la) or a mix of White Scar / Contrast Medium (for the shas'ui)
2. Carefully layer Abaddon Black , being careful to avoid the colour in the recesses
3. Highlight with Mechanicus Standard Grey

Weapon & drone hardware

1. Base with Abaddon Black
2. Wash with Nuln Oil
3. Highlight with Eshin Grey
4. Fine highlight with Administratum Grey

Gyrostabilizers & other gold metal (backpack fins, ammunition)

1. Base with Retributor Armour
2. Shade with Agrax Earthshade between metal parts, and Nuln Oil around the outside of the gyrostabilizers.
3. Touch up with Retributor Armour
4. Chunky highlight with a mix of Retributor Armour / Liberator Gold
5. Fine highlight with Liberator Gold

Lenses & Lights

1. Base with Khorne Red (skip this step for smaller ones)
2. Layer with Mephiston Red on the lower 3/4 of the lens
3. Highlight with Wild Rider Red in a crescent on the lower 1/4 to 1/2 of the lens
4. Fine highlight with Fire Dragon Bright in a thin line at the very bottom of the lens
5. Dab a bit of a mix of Abaddon Black / Contrast Medium into the centre of the deeper eye lenses
6. Final highlight with a tick of White Scar in the upper corner of the lens.
7. Optional: very very faintly drybrush the area light from the lens would shine on with Mephiston Red for an object source lighting effect.

Viewfinders & Screens

1. Base with Stegadon Scale Green (skip this step for smaller ones)
2. Layer with Sotek Green
3. Highlight with Temple Guard Blue
4. Fine highlight with Baharroth Blue
5. Final highlight with a tick of White Scar (only for the 'jewel' style viewfinders)

Skin

1. Base with Russ Grey
2. Wash with thinned Space Wolves Grey
3. Layer with Fenrisian Grey
4. Highlight with a mix of Fenrisian Grey / Ulthuan Grey

Sept Markings

1. Carefully freehand the sept marking lines onto helmets, shoulder pads, guns, or whatever makes sense using Yriel Yellow

I'm not going to bother covering the basing here, as I figure everyone will do theirs a bit differently!