so this is devil may cry 1 right? there are only two ways that he can lose health;
1)jump on him and wack away,his tail usually looses more health,when on top of him
2)this is the best way but also the most dangerous.attack his head!!! but there are number of problems with that:he uses his massive claws if you get too close so watch out for them.And remember when he shoots out fire balls from his mouth,well it's nearly impossible for him to miss if your that close to him,but he does lose more health when doing that way,up to you.
i'm sure you'll be fine mate

'The only time you run out of chances is when you stop taking them...'