Pacing can be difficult. On a hard workout, I find I can go out way too fast. I wear a Garmin watch that lets me monitor my pace and adjust it. Some of the people I run with are really good at setting a pace, so I'll follow them. Getting a feel for setting the pace just takes some practice.
I use Runkeeper for my iPhone. There's this great belt you can buy that holsters it (Spibelt), can't even feel it there. Coaching on how fast you're going every half mile. You can calibrate pretty quickly.
