I think what gets a poem going is an initiating line. Sometimes a first line will occur, and it goes nowhere; but other times - and this, I think, is a sense you develop - I can tell that the line wants to continue. If it does, I can feel a sense of momentum - the poem finds a reason for continuing.
The poem is not, as someone put it, deflective of entry. But the real question is, 'What happens to the reader once he or she gets inside the poem?' That's the real question for me, is getting the reader into the poem and then taking the reader somewhere, because I think of poetry as a kind of form of travel writing.