When I first started running (on C25k) and really struggled with the intervals, I would sing song lyrics in my head over and over as my feet beat the pavement. (I never ran with an MP3 player on my shorter intervals.)
Now that I'm running for longer periods of time - 30-35 mins at a time - my "strategy" is quite different. I've found that my runs are easier when I'm thinking about positive things rather than dwelling on the stressors in my life. I try to list all of the things I could possibly be thankful for in my life. I find that when I'm doing that, my breathing is so much easier and it helps keep my pace up too.
Also, now that I'm running longer periods of time, I do listen to my mp3 player. I mostly play albums that I'm familiar with and love or playlists with nostalgic songs. (U2's Achtung Baby/Joshua Tree/All That You Can't Leave Behind; Radiohead's The Bends; Alanis Morissette's Jagged Little Pill; greatest hits albums by The Who, Bruce Springsteen, Van Morrison (since most of his albums are too slow for running!); The Band's Last Waltz.) I'm also getting into listening to classic country too, as it feels a lot like story hour at the library. Except with whiskey, women, and guns.
At times, when I feel like I want to quit running for whatever reason, I just evaluate myself. If I'm not in pain or feeling dizzy, then I tell myself I'm OK and that there's no reason I can't finish the run. (I also remind myself of how pissed I would be if I ended up quitting!)