Excellent advice so far, the only thing I would add is that the de/dum rhythm isn't always consistent within a line.

Lines can be 9/11 syllables and some feet may not conform to iambic metre - they might be trochaic for instance. There are certain feet that have to be iambic for the metre to work. I think they are 2/3/5 but my memory fails me slightly.

This might cause you a bit of difficulty when you are exaggerating the rhythm.

Another point is that different accents can add or subtract syllables from a word. In Milton's time some of the words will have been pronounced differently and this can cause difficulty for a modern reader.