I think one of the first things you need to do is face the fact that nothing in the current content, be it normal-hardmode-nightmare, needs 2 tanks. One exception might be the 2nd boss in Karagga's Palace - Jorg/Sorna - where you might wanna have some ranged person or an offtank taunting and tanking one of them to take some of the heat at times. I can almost solotank it (as Sith Assasin), but the damage spikes are hard, so I need to be lucky on using all my CD's.
I've done 7/10 Nightmare mode (rest in hard, ofc) as solotank and that is just a bit sad to see, when you love playing a tank and know that there's a lot of us out there. Giving that offtankspot to one that's dps spec, dps-geared and who knows how to pewpew means you go from 4.25 dps to 5 dps and that can be felt!
Next up is the individual gear/optimization of each and every player that you have the ability to affect. Are they running around with the wrong items (eg. Did the Jedi Shadow dps choose ForceMaster items, giving him useless Alacrity). Are each and every one of them doing their own little bit of homework in reading up on theorycrafting and using their characters to the fullest potential? Do they have 2 Rakata Implants/ 1 Rakta Earpiece? No, then they'd better get crackin' on Belsavis Bonus Series/Ilum and unlock the dailies. 5 days worth of dailies is 1 implant/earpiece+1 million creds+5 of each armor/mod/enh mods (rating 50/rank 22 epic = same as the best that standard crewskills can make) for peoples orange gear or the GTN for even more creds.
On that note - Most recently dinged 50's will have orange weapons. Doing the abovementioned dailies gives Daily Commendations. For 8 daily commendations, you can buy a barrel/hilt mod for your type that raises the overall rating of the weapon to 128. They're Epic(51) or Rank 23 barrel/hilt mods. Yes, that's one more than players per standard can craft with crewskills. And you can buy 3 of them with 1 days worth of commendations. Raising the rating means more base dps for weapons = fastest way to gain more dps. Likewise, there's also rank 23 armor mods that raise the ratings of orange armor pieces and give a higher base armor rating (something for tanks to consider!). All these mods are 8 commendations a pop.
During raids - does everyone have stims and adrenals? It doesn't need to be Rakata (but it should, if they want to raid, tbh) but if you know you're maybe going to wipe, buying prototype/blue stims that persist through death is a decent investment.
Also having a Marauder/Sentinel dps'er would mean you have access to a massive dps burst buff (Bloodthirst/whatever it's called on Rep side) that can really mean the difference if it's used 1s before he gets unshielded in P3.. and ofc right after he unshields in P1 to get it moving :)
Any one of these tips could have given you 5% more over the course of a fight.
The Soa fight also gives some easy benchmarks early on on how your dps is - Do you get 2,3 or maybe even more Mindtraps in Phase 2? You will get 2 mindtraps, that's almost impossible to avoid. If you're on par with dps, you should send him into the transition inbetween 2nd and 3rd (for all you elitists out there, this is "only" on normal and yes, it's fully possible to only get two mindtraps in P2 if you have pro pewpew). If you're just waiting for dps to break the 3rd mindtrap and the person sent flying to land before taking him below 30%, then that's just fine also. 4 Mindtraps means Phase 3 will take a long time and you will get enrage. However, it's fairly easy for a tank to kite an Enraged Soa around and if the healers are on the ball and you have a little luck, you can get minimum 1 weakened phase after enrage. I've had up to 3 before he killed the last people off.