Further to my link I thought i'd share the following.
Most techniques described in books and on-line are designed for 1/35 scale kits and dont always work well in 1/72. I've played around with a few techniques but my 'base' approch to 1/72 armour is as follows.
To make this UM SU-100
1. Build all the kit save for wheels and tracks (I find it too hard to paint these in situ)
2. Spray the model with a coat to matt black, I prefer using acrylics for all my spraying.
3. Select the main colour, in this case a dark green.
4. Spray the centre of all the panels in a solid coat but leave the edges / joins black
5. Mist ( spray from a distance) the whole model in light coats until the green panel centres and the black edges are blended into a gradual gradient.
6. When dry spray with gloss varnish and when dry apply any decals if needed, ie turrent numbers.
7. Wash (brush with very watered down paint) the model in suitable filter colour, for dark green I use a brown colour)
8. Pin Wash (less thin paint applied with precision and a small brush) the panel lines and joints in a burnt umber colour.
9. Mist the centre of the panels with a thined lightened version of the base colour to bring a bit of life back to the model.
10. Fit the wheels and tracks after painting them.
11. Matt varnish the model.
12. Weathering can now be done (something i've yet to master!)
Everyone does it differently but I find this general method works for me.
Hope this helps