A few personal ones from the last few decades.... There's a shit load of information on the internet from "two thin coats" to "juicing" to "zenithal undercoat spraying" etc etc. These are ones that I've worked out myself to be useful. Particular favourites marked with an asterisk.
General tactics:
1. Put a layer of soft foam on your painting tray / desk. So when you drop the model you don't fuck it. *
2. Leave the top of the head / weapon tips for last as you're more likely to hold them / rub paint off. *
3.
If you're prone to rubbing paint off protruding sections (I am), then
paint over them as you finish them with matt varnish. It makes touching
up mistakes a bit harder....but still easier than touching up lots of
worn areas. *
4. After doing a matt spray varnish, recoat the metals etc with gloss, or at least, satin varnish.
5. Get a pipette to thin down extra thick paints in their pots, easier than dabbing lots of water in.
6. Paint bases first if they're going to involve lots of dry-brushing /
stuff next to the model's feet. Feet are less likely to mess up than the
base and the base will need less fastidious touching up.
7. When you're starting to paint, take care early on to get the desired level of painting quality, so you've got a standard that's suitable to stick to. I.e. avoid spending 5 hours on Golden Demon-winning undergarments and then realising you don't want to extrapolate that to a 60 hour model to make everything match that quality.
8. For larger / more complex models, avoid getting daunted by the size / timescale by simply applying paint each session you tackle it - don't think about the whole model or even the whole area you're doing, just focus on each paint coat and you can get over "the hump".
Preparation:
9. A thin wash (thinned black or a wash paint) can be pretty useful on the bare metal / plastic / resin to check mould lines and flaws to clean.
10. After the main cleaning a soft brass brush is great for final cleaning / scrubbing to get a smoother surface - on tin-based models only, not lead-based!! *
11. Sub-assemblies - lots of people like separating models into
sub-assemblies, but my general motto: if it's really hard to get a brush
too, it's probably really hard to see, so glue it together and just
make sure there's some darkness inside there. But sub-assemblies can
also be useful to avoid spreading paint on the rest of the model,
sometimes base-coating / shading subs are enough.
12. If you do have sub-assemblies, put a wee blob of blu-tac over the areas that will be glued together - easier to glue and saves cleaning paint off them later. *
13. A useful "mixed" undercoat is a black spray undercoat followed immediately by a faint white spray undercoat, or even a fine white drybrush once dry. This gives a neutral surface, a bit of texture, but dark shadows.
Colours:
14. It can be worth blocking out all / most of the base colours in
thinned down base colour first - it gives you an idea of how a colour
scheme is going to work, and can sometimes reduce the amount of
overspill with later final base coats. *
15. Keep all
mundane areas (pouches, straps, buckles, wraps, handles, etc) in simple
colours with simple painting. They'll look more natural, won't detract
from intended colours, and as "supporting" areas they don't need fancy
painting, just some definition.
16. Sometimes,
especially for batch painting, it's useful to choose a colour scheme
around the paint colours with best coverage. Within reason of course -
no pink orcs - but it can definitely speed things up.
17.
Maybe shade with muted colours or black added to the mix. Shadows are
relatively desaturated in reality so it can look pretty natural.
18.
Maybe stick to similar hues of the mid-tone / base colour for
highlighting - again it can be more natural and usually makes smooth
transitions easier. *
19. Contrast....look at your WIP model with black and white vision. Then you'll see if it has enough contrast overall.
20. If you have a bunch of old inks, and of course at least Nuln Oil
and Agrax Earthshade, don't buy coloured washes for small areas, a tiny
bit of the ink mixed into a new Wash will work well.
Techniques:
21. Just like Quake textures, don't think of the surface as "what am I going to paint on top of this", instead think of it as "what is this actual substance", and that will encourage painting that suits the surface (which obviously can be dyed fabric or painted armour or daemonic skin and thus open to lots of creativity in that case.
22. Make the model angle and the brush work with you - hold and angle the model so you can flow along the suitable painting lines, use the edge of the brush on edges if needed. *
23. Most modern tutorial waffle on about really thinning paint down. Yes this can be useful but equally in the right circumstances (edges etc), straight out of the pot can be fine.
24. To get strong highlights in the right place, paint an area of solid highlight colour within the area you're going to highlight, then blend / translucent layer towards that to get the usual smooth transition. This also is a good tactic for blocking out and planning highlights (and maybe touching up with the previous colour before the blending stage).
25. Metals can work great with Washes (almost cheating, they're so easy), keeping the shadows matt as the metal wouldn't reflect light there, and some small bright highlights on edges and points that would reflect the light. Thinned paints dabbed on can provide a nicely dusty matt rust effect too.
