There was a story about Kevin Colbert a couple of years ago about his draft strategy. Essentially, the Steelers compile "Draft Bubbles" of 12 players that they feel (from doing multiple mock drafts amongst staff, from memory) will be available around the Steelers pick. They then prioritize each player from 1-12, and scratch off each name as they are removed from the board on draft day. From memory, there was something about guys they felt would not be available being placed in a seperate bubble, and they get consideration if they fall... but a bit hazy on the details.

As to how the Steelers prioritize- although they haven't said it, pretty sure steelz09 has it right- BPA at a position of need. So, because the Steelers have, say Pouncey at OC... then OC isn't a 'need', and therefore all OC's are off the board... but because NT is a 'need', they'll look at the BPA that is a NT..or a Safety...WR..RB...up to 12 players.