The golden rule according to traditional singers we've interviewed is to "sing as you say where possible".
One way of getting it right is to talk through your text a few times first, then alternate with a line sung and a line spoken, then half a line.... etc.
Usually comes right in the end.
Biggest pitfalls are singing to accompaniment, as has been pointed out.
Learn the song without (maybe it works better that way anyway), then add accompaniment; but make sure accompaniment follows and doesn't lead.
Jim Carroll