Alright...
It's pretty easy as soon as you get a strategy on enemies and know who to priority. Sometimes there'll be many enemies, and you know you can't kill them before they DT. Take down the ones who gives the most trouble since they will give you nothing but more trouble when they are in DT.
With Nero, practice your exceed abilities and Max Act.
Streak with level 3 exceed ain't that good against bosses as they are used against masses. If you want to use a level 3 exceed attack against bosses I reccomend either Shuffle or Calibur due to their more concentrated and accurate damage.
Charge your gun at all times, if you can't charge it that good with the normal setup, change the setup so you can more easily charge the gun. A charge shot level 3 is a savior at times.
Know what you are doing. The enemies attacks hasn't changed, just their groups, health, damage and the included DT. You should have a knack on your tactics for each and everyone of them.
The buster moves often leads you out in the open. I don't rely on it that much since I feel weak to take advantage of something like that. DT + busters on bosses are exceptions though since it's awesome.
For Dante, learn to use his weapons. To rely on single weapons through the whole difficulty ain't that good.
Use Lucifer for support, letting it's arrows or whatever it is to keep the enemies at bay and use their timed explosions to your advantage to hit in a combo. Pin-up is a great move. It deals gigantic damage and never stops raising your style. Use that to your advantage.
Gilgamesh is slow but it's power is high. Kick13 is a good way to knock enemies in the air as a start up combo. Straight is good to use as a counter move or a move to use directly after Kick13. The main idea with Kick13 is to to knock enemies temporarily. You can use Rising Dragon (down + style button) after a Kick13 with the Devil Trigger trick against Mephisto's, Faust's, Blanco angelos, Alto angelos, Mega Scarecrows to kill them instantly.
The Devil Trigger trick:
Use DT in the middle of the Rising Dragon attack to deal extra damage. If you DT in the start of the attack and then in go out of DT in the end you can deal gigantic damage.
That's just a part of what I can learn you. Too much to write. T_T