1) join a running group / club. Everyone starts off somewhere so don't worry if others are much better when you start. Distance running is often a lonely pursuit and having others around you can motivate you on days where you cba
2) in the winter months run lots of aerobic work (now - mid march). This takes time to build. Try a mixture of easy runs, tempo runs, 5k focussed intervals, long run once a week (50% -100% longer than your other longest run). Add in one faster session each week in the winter so that you keep in touch with your speed - hill sprints are good for this. Max number of three sessions + one long run per week
3) in mid December start running one anaerobic based session per week. This can be fused with your tempo session (I.e. 4 mile tempo + 5x400m)
4) in mid march bring in faster sessions that are 1500m focussed (10x400m, 4x800m etc - there are loads of examples on the internet).
5) start racing late April / early May. Try and get a race in every two-three weeks through to September. Race distances from 800m to 5,000m to complement your 1500 / mile races
6) try riding on a static bike instead of easy runs when your legs are feeling injured / more tired than usual. It's a non impact way of keeping the aerobic work going.
7) eat healthy. Eat a range of foods & avoid junk food where possible. Don't try and diet (avoid carbs) at the same time as trying to increase performance - you'll just burn out. A healthy diet + exercise will shed any unwanted pounds
8) keep motivated. Sometimes you'll feel like your performances aren't progressing as fast as hoped. Dust yourself off and get back on the saddle. The performances will come with time - be patient
9) make sure you have an inhaler that is suitable for your exercise - not sure if you'd need a stronger prescription if you are active...
Way back when I was a nipper (8 - 10 y/o) I ran faster than 6 minutes for the first time off the following exercise:
Mon 1 hr swimming
Tues running session with club
Wed 1 hr swimming
Thurs running session with club
Fri 1 hr swimming
Sat morning running session / xc race
Sat evening 1 hr swimming session
Sun easy running / xc race
Good luck!