well it depends on gear and what your purpose of the specc is, ie fast leveling or keep on raiding for a while.
I would suggest filling up in;
Fel concentration Nice to decrease the chance of interruptions while casting SD, haunt etc.
Soul Siphon, this is more situational since it's more playstyle oriented. Nice way to keep up Mana/health imo
Malediction, Increases grp/raid dmg extra and increases your dmg nice one imo
Death's Embrace, increases survivalability and increases your shadowdmg with ~4%
i would drop points in;
Only put 1 point in Eratication
and loose 1 point in Shadow embrace,
With Haunt and so on, you won't have too much time to cast Shadowbolts, so i thought pushing immolate is better than isb.
Well I'm not sure how many but I think you'd get a few SB's away during the fight. I heard some1 talking about the Imp SB only improving SB direct dmg not DoT but I'm not sure. If I would skip Imp SB in my specc it wouldn't end up in MC anyway since i don't think the dmg increase is enough to grant it 1-2 points..