Interval training is your friend. There are several ways to do it.
If you like to run outside, try this - Ladder Intervals
1) 1st mile is for warm up
2) Then, at 1 mile mark - Sprint 30 sec, slow 30 sec, sprint 45 sec, slow 45 sec, sprint 1 min, slow 2 min, sprint 1 min, slow 1 min, sprint 45, slow 45, sprint 30, slow 30.
3) By now, you'll be around mile 3 - if you wanna do that series again, go for it.
4) Last mile, cool down.
On the treadmill, its all about inclines, not speed
1) Take what you normally run at a med-hard pace, in pace, for example, 7 minute mile. Add 1:30 to that pace, say 8:30 per mile.
2) You'll run this speed the whole time.
3) For the first mile 1% incline
4) For the second mile 2% incline
5) At mile 2, increase to 5%
6) Mile 2.5, back to 2%
7) Mile 3, increase to 8%
Mile 3.5, back to 2%
9) Mile 4, increase to 5%
10) Mile 4.5 back to 2% until 5 miles - then warm down.
These types of intervals are wicked for increasing your running speed and endurance.
