I'm loving the new Demo personally, the changes have really upped its overall viability and it's still just as fun as before.
I glyph for Metamorphasis, Life Tap, and Quick Decay
Glyph of Feltard is pretty good too, but I prefer the 3 above
The main source of your damage as Demo is vigilance and procs. Vigilance in keeping up Immolate and Corruption 100% (CoE is a good one to keep up too!), and Molten Core procs. Popping your Demonic Empowerment every 42secs and your Metamorphasis whenever it's up (or when there's a burn phase eg. BLust) is obviously going to up your dps, but knowing when to cast what is the big thing w/ Demo.
Molten Core Procs:
Since this buff procs from Corruption ticks, glyph of quick decay is amazing and using your spellstone over the firestone goes without saying. You should be casting Shadowbolt to keep up your 5% crit effect on the target whenever you've got all your DoTs up and etc, but if there's a Molten Core Proc you've got to use it up with three Incinerates.
Decimation Procs:
If there's adds running around anywhere that you can pop a SBolt or Incin off at during the fight to gain the Decimation buff, DO IT! I was getting tonnes of procs on Saurfang the other night before I switched to Destro for the stuns. Right now, the Decimation buff isn't used up when you cast Soul Fire... whether this is going to be fixed or working as intended, I don't know really. Either way, getting 3-4 Soul Fires off is a HUGE dps boost especially when there's a Molten Core proc up simultaneously (they'll be hitting for 15-30k).
When the boss itself is below 35%, make sure you're still keeping up your DoTs but now you have to make sure that you're also keeping up the 5% crit effect from 1 shadowbolt every 20-30secs as well as spamming Soul Fires when you've got Decimation procced. Since Decimation now also procs off of Soul Fires, you should be pretty much chain casting Soul Fires
.
Essentially:
1.) Keep up Dots & a Curse (CoE if there's no UH DK/Boomkin/Other Lock, CoD if there is, or CoW if there's no ArPen effect/AP reducer (which there always is anyway), or CoA if you're stylish like that).
2.) Use cooldowns: always use Demonic Empowerment when it's up, use Meta whenever it comes up or save it for a burn.
3.) Keep up 5% crit buff from SBolt (this is also your main spam ability).
4.) Use Molten Core procs: Incinerate if >35%, Soul Fire if you have the Decimation buff ALREADY up on you (can't waste soul shards!).
5.) Use Decimation procs: Watch that sucker burn!
Please, comment or criticize if I'm making some awful mistake.
Hope what I've said is of some help!