In general, the secret to DMC is to be cautious. Despite all of the cutscenes telling you what a bad-ass you are, the easiest way to win is still divide and conquer. Try to trap enemies against walls for deadly comboing. Keep yourself away from the majority of the enemies if you can help it. Always try to limit how many enemies you fight at a time. If things are getting crazy, Air Hike/Trickster the hell out of there. You don't need mad combo skills to win, you just have to be observant and efficient.
That being said, I was able to beat Cerberus with the pistols. Basically, I just stood at a long distance with E&I, and fired like a madman. His attacks are pretty easy to read, so you just have to react accordingly. The most annoying one (raining ice) can be predicted by observing the floor. The floor will get "frozen" a moment before ice rains down. I used the Trickster dodge to avoid most of his attacks. Whenever he lunges, dodge, then get in good with Rebellion (Sidewinder) for huge damage. Don't forget that you need to clear off the ice from him before you can damage him.
Don't be afraid to use a healing item if you need to. Unless you're going for all S ratings on your first time through, one item use isn't going to screw up your rating. I've gotten A's so far, even though I've used a small green star on every boss.
