Advanced techniques: some of these are common practise and some of them may be unique to me (well they won't be if you use them, but that's the idea).

Filling large holes:
My method for filing large holes is a little unorthodox though I only use it on holes that it would be difficult to cover over with plasticard or fix with some other technique. First I take some soft balsa wood and cut it so it's a bit big for the hole, then I apply some superglue to the balsa wood and squash it into the hole (the softest balsa possible should be used so the force needed to get it in doesn't damage the parts). Once the glue is dry I cut off the excess balsa wood. I then file and sand the surface of the wood plug to the desired shape and coat it in more gap filling superglue. When this dries I file and sand it. Sometimes it takes a few coats of super glue to get a smooth surface. The big advantage of this method is that it can fill large holes in about 30 mins and it is quite light unlike epoxy putties that can take a long time to dry and be rather heavy. A word of warning about painting: you need to use some form of undercoat if you use acrylic paint because it doesn't stick to well to the superglue.

"Shadow painting" I don't know if this is the correct name for this technique but I do know that many other people use it (most of the best mecha modellers in fact). This technique takes advantage of the fact that airbrushed paint is slightly transparent if sprayed on lightly to create realistic graded shadows. The undercoat is the most important step in this technique. The model is first painted either light or dark under coat and then the shadows (if you used light under coat) are sprayed in using black or the highlights (if you used dark undercoat) are sprayed in white. Either way you have some very harsh and sharply defined shadows or highlights. The actual colour that the model if meant to appear is now sprayed on lightly so that the shadows or highlights show through. The intensity of the spray and the number of passes over the model determine the extent to which the shadows etc. show through. It is best to err on the side of caution and spray to little paint because you can always put more on if it isn't enough. I used this technique for the first time on the RX-178-II. This technique can also be done with a spray can but the shadows/highlights have to be created some other way before you spray over the top and there is less control (I haven't tried this method but I have read of it).

Pastels:
I bought some pastels and watercolours to give my mum for her birthday one year but I had read you could use them to weather models so I tried them out first. Needless to say she didn't get the pastels. Chalk type pastels are basically just coloured pigment powder and make very convincing dust and soot. I first tried them to do the exhaust blackening on the T-72 (after I took the photos I'm afraid) and they worked well so I did the burn marks for MSG0x's battle damage using them. They can also be used to make things look dusty like tanks in the desert of rally cars. The pastels can be applied normally but I use an old brush and crush a bit of pastel first. Then I dip the brush and scrub the pastel onto the surface this technique is better than using an airbrush for smoke blackening etc. as it uses a dust just like smoke and doesn't spatter drops like an airbrush. Varnish needs to be sprayed onto the finnished pastel work so that brush strokes dont move the pastels around this also stops the pastel from rubbing off.