Painting small figures effectively is not easy, but, for what it is worth, here are a few tips developed over several years.  A small figure is, in effect, a large one seen from afar - to seem real it needs to be lightened (the scale/distance effect) and the detail accentuated.

Brushes:  For Enamels, it's worth investing in sables, since you can clean them, though they are often overpriced for the quality.  Acrylics clog the root of any brush, so I use Pro Arte nylon, which are cheap enough to be replaced regularly.  The important thing is to have a perfect tip - I sometimes trim mine with scissors.

Paint:  Enamels (Humbrol) are extremely fine nowadays.  The disadvantage is that you have to wait a long time for each coat to dry enough to prevent lifting with the next colour.  Being impatient, I use Acrylics, except for metallics.  The Humbrol range dry very fast, but have a limited range of shades.  The Vallejo range are impressive, although some of the colour names are more imaginative than accurate.  I do not care for Tamiya - the spirit solvent makes them difficult to mix and the smell disagrees with me!
The colour numbers suggested are from Humbrol Acrylics.

My Technique:  Stick each figure to a small block of wood with Superglue.  I use 2 inch sections of broom handle.
Start with a thin white Enamel undercoat - let dry (a minimum of 3 hours).  Then block in the basic colours, remembering to keep the colours light, with maximum contrast.  I usually work in the order:- Flesh, Uniform, Boots, Equipment, Weapons.  A size 2 brush is usual.
When all the colours are on, line out with a suitable colour: for German figures I add gloss black to field grey.  Each part of the figure is defined by a very thin, dark, glossy line.  For this you will need a '00' brush with a fine point.
The face and hands are defined with a reddish tan (gloss tan + scarlet).  A touch of dark brown for eyes, mouth and any visible hair.
Tidy everything up and finally add any insignia.

British Uniforms:  The best book on the subject is 'Brayley & Ingrams - The World War II Tommy', Crowood Press, ISBN 1 861126 190X, packed with colour photos of the real thing.  British kit was very standardised and I suggest the following colours for painting:

Battledress:  KHAKI  No. 26: add a little black to the base coat, and a little white for highlights.  Vallejo No. 880 KHAKI GREY (sic) is also excellent, and does not dry so fast, allowing a little shading. For  Canadians, add a little LIGHT OLIVE 86, as their uniforms were on the green side of khaki.

Webbing varied from Light Straw to Mid Green - I prefer the light colour since it contrasts better:  KHAKI 26 + WHITE + YELLOW 24 (1:1:1).

Helmets, if ungarnished, a deeper khaki - add a little DARK GREEN 30.
Garnished: KHAKI + BLACK to make a deep drab. Pick out net and garnish with Light Khaki (same colour as webbing or lighter).  The scrim strips: LIGHT OLIVE 86, BROWN 186, and wash the shadows with GLOSS BLACK/KHAKI mix.

Boots:  Paint them KHAKI, then overwash with BLACK - this gives the effect of a dirty boot!

Lining Out:  Thin mix of GLOSS BLACK + KHAKI   - apply with a very fine brush to all the cracks.

German Uniforms:  The Germans started the war in very standardised uniforms, but the situation deteriorated, so one has the impression that by '44 there were scarcely two men dressed alike.  I cannot recommend too highly a good reference book, and the best I have seen is "German Soldiers of World War Two",  by Histoire & Collections ISBN 2 908182 297. This is a full colour bible of original items photographed on live models,  and is indispensable.

Field Grey varied a lot, but I find LIGHT GREY 64 + DARK GREEN 30 (1:1) pretty effective.  Late  war items were greyer than earlier, and officers' tunics tend to pure grey (LIGHT GREY 64).

Helmets:  DARK GREY 32. You can add sand or green splodges for individual camouflage.

Leather Equipment:  SATIN BLACK 85 + a touch of Red.

Bread Bags:  LIGHT OLIVE 86, KHAKI 26, DARK GREEN 30.  I recently saw a stack of these at a trade fair and they were all different.

Gas Mask Canisters:  DARK GREY 32 or BLACK GREEN 91.

Entrenching Tools: MATT BLACK, NATURAL WOOD 110 handle. The carrier could be SATIN BLACK 85 or DUNKELGELB (Humbrol ENAMEL 93).

Water Bottles: BROWN 186. BLACK or DARK GREY cup, BLACK strap.

Boots:  Try DARK EARTH 29 and wash over with BLACK.

Zeltbahns, Army Camo Suits, Helmet Covers:  All made from the same material - the two sides were a slightly different shade and batches varied anyway.  Try KHAKI+WHITE+PASTEL GREEN 36 (2:2:1).
Red Brown splinter pattern: MATT BROWN 186 + touch of BLACK.
Green patches: DARK GREEN 30+PASTEL GREEN 36 (1:1).

Panzer Uniforms: MATT BLACK 33 + touch of WHITE - this allows lining out with GLOSS BLACK.

Weapons: SATIN BLACK 85 +touch WHITE  -  again, detail can be picked out with GLOSS BLACK. 
Rifle stocks:  MATT LEATHER 62 and GLOSS SERVICE BROWN 10, 1:1 mixture.
MG42 stocks were usually Black plastic.
Ammo tins and drums: BLACK GREEN 91.

SS Uniforms:  Three orders of dress concern us here:-
1)  The basic field grey uniform, identical to the Army, save the insignia.
2)  The '43 universal camo suit, identical in cut, but made from the "Pea-Pattern" fabric.  (Our Wehrmacht list figures can be painted as both of these.)
3)  The oversmock (SS list figures): this came in several patterns.
I recommend referring to colour pictures for (1) and (2) to get the patterns right, but the colours (which varied considerably in strength of tone) can be as follows.

'43  Pea-Pattern Suit:  Base colour BROWN 186+FLESH 61 (1:1 mix); overspotted with clusters of spots in BROWN 186, PASTEL GREEN 36, and BLACK GREEN 91.

Oversmock: Base colour BROWN 186 + touch RED. Spots merging into solid patches of PASTEL GREEN 36 and BLACK GREEN 91.  There was also a late 'water' pattern where the same colours blurred into one another.

Insignia for German Army & SS:  BLACK GREEN 91 'Badge cloth' for backing of eagles, shoulder straps, etc.  WHITE +LIGHT GREY eagles, piping, buttons, etc.

Anthony Barton