Share 'Classic lines - Body!'

Ok, so I just finished the sleeves for the cardigan, which I knit on dpns - presumably that was ok because they worked out fine.  Now to the Body!!  This is my first time EVER knitting a sweater in the round and I am feeling a bit daunted by it all!  Any hints and tips?  I see from looking at the construction of some peoples cardigans that they have put in a line marking the waistline - or am I j…