I take advice like this to heart, so I thought I would share some of his thoughts on Dark Eldar modeling.
The first was that when modeling, avoid any customizations that could easily be placed with a different army. For example all the fun spiky bits of chaos are often very easy to place where they came from without doing a little bit of work on them. It is OK to use bits from other armies, you just do not want your army to be Chaosified or look like a different army..
Icons are for Chaos. Chaos worships them and use them as symbols. Where a skull motif is used, instead use something a little more literal like the skull of a recent prisoner with the spine still attached. Stay away from bestial imagery (like stone, metal gargoyles) or daemons. Skulls of the defeated are great, but nowhere should you see something crafted to look like a skull. The same goes for Gothic angel or cherub imagery.
Spikes, skulls, hooks and other things involved in torture, pain, and suffering work great. Just avoid the obvious other army look, and you are doing fine.
I know some of this repeats, but I always find myself pouring through my bits regardless of what I am trying to accomplish with my armies and grabbing anything spikey with skulls on it. Regardless though, the final thought on this is, that it is your models, and that everything I just mentioned is an opinion. I just do not want my Dark Eldar to become Chaos Eldar.