Most important point to tanking as a Dark Knight and pulling a boss:
If you learn NOTHING else, this is THE single most important tip you'll be getting:
Never. Ever. EVER.
N E V E R pull with Plunge or use Unmend>Plunge under any circumstances ever for any reason unless you're pulling A5N or A5S.
Never.
I can't stress enough how infrequently you should do this and how frequently I see people do this.
Stop.
Do not do it.
Ever.
Please.
"But, why not?"
Multiple reasons:
1. If you have a WAR or NIN in the party, you're wasting potency by using it before SE+DE.
2. If you have a DRG, NIN, or MNK, you're forcing them to lose potency by using gap closers on the pull or because they have to run for an additional 1-2s to get to the boss especially when you then proceed to pull the boss all the way north when they shouldn't be tanked north to start anyway.
3. See: 2. It's the most important reason.
4. Positioning. Every single boss in the entire game right now (aside from Ratfinx) should be tanked in the middle of the arena or near the middle when the fight starts. If you plunge to a boss, you force yourself to then have to run backwards to bring it there, missing autos and potential parries as you turn your back to the boss. If you Unmend and delay your run, you can meet the boss in the middle and have it positioned immediately without having to run around. Melee dps can also just run in and meet it middle with you! It's almost like this is how you're intended to pull bosses!
5. See: 3.
6. Animation delay after Plunge (if not used fast enough after Unmend) can cause you to have dropped GCD time, which is a pretty significant loss in the long run.
7. You should be pulling in Grit. You're taking a hit on damage for Plunge when you can use it later at normal potency.
The way I tend to pull as DRK is:
Unmend>[LB]>HS>SS>PS>[DA+drop Grit]>HS>[BW>CaS]>SS>[DP>DA]>SE>[PL]>S>[SE]>HS>[LB>DA]>SS>SE
Salted can probably be dropped pre-pull, but losing the initial shot of Grit damage for a delayed non-Grit SE feels better to me. After that SE, you can slap Grit back on if you feel you need more hate - it's very unlikely you'll lose hate through those two combos, and I generally will just use a PS either in place of the SE there (usually keeping the DA because BW is up and if I need it, I want the (marginally) bigger lead) or as he next combo not shown.