I'm assuming you mean with Nero? unfortunately they're one of the more difficult enemies with him.
I only really know a couple of ways to get cheap shots and it's all about the Buster but you prob already know these, like as they spawn if you are quick enough you can get them with High Roller and it will get them on their back for a Buster grab (not very useful when there is a lot of enemies but if it's just one Angelo and a couple of Bianco you should be able to get it without being bothered) alternatively as they do their dashing sword attack, I believe Neros DTE? would knock them up so you can get another Buster, other than that just get in as many Charge Shot 3s as you can and Buster their shields as much as you can (it damages it a lot)
As Dante they are a bit easier if you don't mind taking a couple of hits. Use Omen as it takes away their shield even when it has no charge and on DMD. Just go DT so you don't flinch and use it then and when their shields are gone use a quick Beast Uppercut followed by Distorted Real Impact and it will kill them. Make sure you Distort just before the second hit of Real Impact as it does most damage that way.
Beast Uppercut followed by RI is a really useful broken combo that will kill almost everything and comes in real handy in DMD or BP if you want to race through the early levels to stock up some time for the later ones.
As far as general DMD tips it really depends on what part of the game you're at and what enemies are there, every part has a different tactic. But if you are playing as Nero make sure you have shoot mapped to the right trigger so you can charge shot regularly.
Well done for beating Credo, don't worry if you can beat Agnus on mission 6 you can do anything in that game!