Two longish look-ins:
"In today's Wall Street Journal (online subscription required) Sharon Begley provides a rare look into the world of academic journal rankings. She describes some of the ways that scientific journals manipulate their "impact factors"."and later describing his/her (I would imagine people know, but I won't out anything) own experiences (I would add to his below comment by saying I would be surprised if anyone who has published a few papers has not had the reference coaching happen now and then).
"One [way] is to ask authors to include additional citations to other pieces in the journal. I've seen this tactic used several times (both on my pieces and on those of colleagues). Typically, once a piece is either accepted or in the "last round", the editor might "suggest" other articles in the same journal which might possibly be cited. In one case, the editor gave a colleague of mine a list of eight possible citations (which would have increased the total citations in the author's bibliography by almost 50%). However, this doesn't happen as much as you'd think, because I use my bibliography as one of the criteria I use in deciding which journal to submit a piece to: if I cite a good number of articles from a particular journal, it's probably a good fit for the piece"