I was asked a similar question on another forum, here was my reply
So what is Dipping?
Dipping began as the technique of taking a figure in base coat colours, and submerging it into a wood-stain. The excess wood stain has to then be shaken off, then the figure is left to dry, and (should) be of excellent table top quality. After some experimentation the technique developed from a 'dip and shake' to a 'paint the dip' when the stain is applied in a controlled fashion with a brush.
Dipping Tips
1: The figure has to be dust free. That means that you should probably not dip something that has been lying around for a while.
2: The figure has to be mounted on a sturdy base. It will have to take some serious shaking/spinning.
3: The wood stain is best used outside, due to the odour, and the spray caused by the excess dip.
4: When Spinning the figure, do it pointing upright rather than down.
5. Don't bother painting on the eyes before you dip, they get drowned in stain and you have to paint them on again later.
6: When making larger models try dipping the pieces separately.
7: Unlike model paint wood stain is not water-based, if it is too dark for you then you can use white-spirit as a thinner (too much can cause the glaze to crack though).
8: Too much dip can accumulate in some of the larger crevices on a model (welling up), a brush can be used to remove the excess dip before it dries.
Looking at the larger flatter expanses, there are two problems.
7. The dip has to dry whilst the surface is flat. Otherwise, it will pool
8. The dip has to be removed from the surface evenly. Otherwise, it will streak
New-Wave Dipping
A later development in dipping resulted in no actual 'dipping' occurring at all, the stain is merely painted on with a brush, allowing you more control and the ability to use different shades of dip on different areas. In essence it is the same as if you were 'inking' the model only thicker (any excess still needs to be removed though).
Once applied remember to hold or support the model upside down for the varnish to run upwards into the higher recesses of the miniature. Before 10 mins is up, turn the model right way up for the excess varnish to settle downwards again.
As a final note the new GW washes work really well and I personally prefer them to dipping because you can use various colours on different areas. Or if speed is your thing then brightly painted models washed with badab black is very quick.