1. Stick with a "spender" skill and roll it on boots/other pieces (I'm only familiar with Wizards) until it's perfect. Ex: my wiz is mainly using Arcane Torrent, so I rolled +15% Arcane Torrent damage on my boots, +15% Arcane Torrent damage on my hat, and 15% Arcane Torrent damage on my source, too.
2. Elemental damage, elemental damage, elemental damage. I have +20% Arcane Damage on my neck piece, +20% on my bracers, Andrial's +20% Arcane, +20% Arcane Stone of Jordan, +15% from Gesture of Orpheus, and a +10% Triumverate. I have +105% raw Arcane damage, and that Gesture rolled almost perfect on dps, so my arcane torrent is doing 573% weapon damage, plus 45% base damage from my hat, boots, and source, plus 105% from my elemental stuff. So my Arcane Torrent is doing 618% weapon damage + the modifier for Arcane Damage, and I'm not sure how that's calculated, but I know it's a lot and I kill things fast.
3. Make sure that your Paragon Points are being spent correctly. For literally every build that I've seen, +Crit Damage is going to outweigh anything else for sheet DPS, and I think for actual DPS, too. There's just not a lot that beats a +50% boost to every crit you make. So when I crit, I'm doing 723% weapon damage + crit damage, which I'm sitting at 400% right now, with 40% crit.
My sheet DPS without buffs is just under a million, my toughness without buffs is about 4.5 mil, and I can bot Torment 3 and literally melt anything that comes at me. I also have a Coutness Julia's Cameo, which makes Arcane Enchanted into an actual healing method, so I was able to get rid of a lot of toughness-gear. I'm trying to a good Blackhorn set so that all the nasty ground effects null, too. Just need three good pieces (boots, pants, chest probably?) and a Ring of Royal Grandeur.