If you wanted to paint any of your kit, a relativley simple and good looking technique is to use leaves like a template, I do this with large pieces of kit that have solid colours (like a plate carrier in OD for example) the trick is to lay a few leaves on top the kit in desired fashion and start of with a medium to heavy layer of spray paint then move the leaves around and use lighter and lighter layers, choose which ever base coat you feel fits the current colour of the blank kit and then use other colours to make up you camoflage scheme, so you could have a base colour of light green than move to patches of dark brown, black, tan, and a few dappled spots of a sand colour, the great way about painting like this is the custom look you get afterwards.
For the worn look, you can either kick it around in gravel like Ian_Gere suggests, or use scotchbrite, lightly rubbing all areas and concentrating more on the edges of pouches ETC, you can even use a wire brush on those areas, just don't go too mad as you'll easily wreck the kit your working on.