It depends on your level of painting and what your hoping to achieve to be honest.
The easiest way would be just to highlite the extreme edges of the armour with scaley green or you could blend mixes of black and green slowly up to give a richer depth but this takes time and practice.
Washes will work to a degree and if you want a quick and easy finish.
With the metal I find a metal base with a deep purple wash then a quick highlite of metal looks good on Dark Eldar weapons.
<img src="https://www.heresy-online.net/daemons/adoptables/888.gif" alt="Broken Daemon Image" /><br><a