Definitely get all of your steering componentry checked and replace if required; ball joints, tie rod ends etc.
From there it depends how hard you wanna' go at it and also take into condieration how much you want to lower the car by.
Castor bushes are prone to going - replace the bushes or buy adjustable castor rods. Remember Skylines LOVE more caster, so I'd go rods. When you lower Skylines you generally induce a fair amount of rear negative camber so I reccomend replacing the upper control arms with adjustable camber arms and as a result you may run out of toe adjustment in the rear, so whack some toe rods on as well if necessary.
There are four large fluid filled bushes in the rear subframe, these are prone to going and are a pain in the ass to change. You can get rear subframe collars cheap and they are easy to install, these basically lock the OEM bush into place. For comfort put polyurethane bushes in (SuperPro do a kit) but if you don't mind the odd clunk and a bit more performance replace with alloy bushes.
That'll be a pretty decent general suspension freshen up without going overboard.
Or HICAS lock washers do the trick and go under the radar