What distance do you want to break 8 at?
I started running this winter by doing intervals on a treadmill. Nothing to tricky, just moving. When I hit the streets in April, everything changed. I began with a 2 mile run, bumped to 2.5, 2.8, 3.0, 3.5 and eventually 4.5.
I found I was able to build speed easily when the 3.5 loop got comfortable. I do the 3.5 mile route 2-3 times a week, and 8 min miles are the norm. I save the 4.5 for weekend days, and I'm lucky to pull an 8:30 from that route.
I'd look online for some 5k training routines. Most of them include some 400 or 800 m sprint sessions that will help you get your speed up.