fartlek training is a good way to increase fitness and speed because it involves sprinting and jogging. fartlek is a sweedish word for 'speed play'. its all about increasing the intensity over a period of time and then lowering the intensity so you can recover. when recovered increase the intensity again. a basic session of this would be (on the treadmill):
5mins jog to warm up etc - 9kph
1min run at 15kph
1min30sec rest joggin
1min run at 15.5kph
1min30sec rest joggin
1min30secs run at 15kph
1min rest joggin
1min30secs at 15kph
etc etc etc
just play around with the speed, jogging, running, sprinting etc. when running outside you can use markers to determine when to increase and decrease your intensity. for example, sprinting between trees down the road (its much better doing it outside personnaly)
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some helpful advice:) 
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