The world famous "motivation" problem, we've all been there...(this is what i do)
i focus as hard as i can using my imagination, i pretend that I'm in a platoon and going out for the morning jog, i also add the fact that, theres a platoon leader (Sergeant, master coporal, what ever...) and (he or she) is yelling (his or her)guts out at the platoon, and to add more pressure, last one to finish line gets to do it ALL OVER again,
so you wanna make sure that you keep running, and DON'T STOP, it doesn't have to be a sprint to the finish line, just go at your own comfortable speed and stick to it.
i HATE running! But its the army,right? so you gotta do, what you gotta do.
So far it seems to be working with me, Ive been lifting weights for 10 years now, but never did any cardio up until september.
i could run for about 5 minutes and be full of cramps and out of breath, so once i hit that feeling, i slowed the pass down so that the pain went away and i got my heart beat back down a bit, once i hit that comfort zone again i started a little faster again. so i went from running to a light jog and back to running again.
today i can run 4 miles none stop in about 32 minutes, and sometimes ill go 6.25 miles in about 50 minutes.
give that a try and you should be fine. ;D