Label it highhhhest priority just because the email program lets you choose that priority.. Write URGENT three times in subject line in bold, red. Thank, apologize, thank, apologize 33.5 times throughout the email. Write long-winded story about what you need instead of to-the-point simple request. Be exceedingly obliged even before the favour is done. Like write off your life or something in return. Thank in advance and in nervous, feverish anticipation. Fail to realize that the person has a life and is well-aware that this is not earth-moving stuff,and will probably never take you seriously. CC it to all the email accounts of the person that you are aware of.
I'll get to it when I get to it. Go take a long hike.