B.R., you'll have to post some tutorials on that. Those are some of the biggest complaints I've heard on this one, and lately I've seen more 12" figs with loose joints than not.
My biggest priority in tightening joints, aside from tighter joints of course, was to be able to recover what was original if I wanted to do so. This meant I wasn't going to be drilling additional holes, adding screws, or anything of the like. This also meant that the super glue option some people use wasn't practical either. After I'd removed the body glove of the trooper I noticed the offending joints generally had wider gaps, or more give, between the pieces that make up the joint. I ended up cutting and shaping aluminum pieces from pop cans and shoved them in the gaps thus adding surface friction between the joint pieces that the original joint lacked. I made the size of the aluminum offsets small enough such that, once placed, their edges wouldn't come in contact with the body glove. I found the dull side of a scalpel blade worked pretty well at pushing the aluminum pieces in place. Depending on the severity of looseness in the joint, more than one piece of aluminum, stacked one on top of another, may be required to "fill" the joint. This method allowed enough strength to tighten a knee joint to the point where my Stormtrooper can now stand, unassisted, on his own, whereas before he'd topple over like a rag doll.