Weathering really depends on the individual as some people like clean figures and others like a little to a lot of weathering, myself I like the figures to have a real gritty look to them especially if they are suppose to be fighting.
For weathering their are a number of technics that can be used and they are ,
1: Weathering using paints, you can actually get good weathering using paints you just need to pick the correct colours, for example if you have a figure on a base with a lot of dirt you would use say a Beige Brown with looks great when dry brushed over the figures it gives them a nice dirty look.
2: Washes are also good for weathering but to get a really good weathering to the figure you sometimes need more then one layer which needs to built up over the layer before.
3: Pastel Chalks are my favourite and IMHO is the best way to go as the pastel chalk sanded or lightly scrapped of the chalk makes a fine dust which can be applied using a thin brush depending on the size of the figure. When applying the chalk you just apply a little and this will get in creases etc and give a great look that the figure has seen some action and there are a lot of different colours.
I hope this helps mate and if you need anything else just ask.