For me it’s about knowing the translation really, REALLY well. If I understand what the other person is saying to the point where I don’t have to stand there translating it in my mind, then I can respond more out of conversational impulse rather than memory, and if I know how the conversation goes, I can just speak it in Italian (or whatever) instead of English. I do sometimes find it hard to avoid being TOO free with the rhythm though – I always have to speak it in rhythm a million times to get that aspect down and then add some rubato later.
I agree with Greg! I’m working on some Mozart recit right now, and it’s also helpful for me to understand the harmonic progressions and accompaniments going to really give the language a shape in my mind. I don’t get too nitpicky about remembering my theory classes from school, but remembering that the composer really had an expressive idea in mind when writing those phrases helps, even though it can seem repetitive and formulaic.
For me, what I have learned is that each composer had a different idea when he wrote recitative. So in order for me to do recitative I must know which composer wrote it. Then I look at the music and determine whether the music is reacting to what I’m singing or if I am reacting to the music. I also look at what was before the recitative, so I know why I’m singing what I’m singing. Recitatives are sometimes harder for me than the arias.