Aerobic work.
Aerobic work!
AEROBIC WORK!
Anyone that has a decent mileage base, (In my opinion 35 Quality / 50 Semi Quality / 70 Junk miles per week) can break 2:10.
You don't really need to worry about all of the fancy shmancy 800 stuff until you are under 2:10 in my opinion.
This winter just make sure you run at least 5 miles every day, (but try to do more) and do a speed endurance session once or twice a week.
My favorite 800 speed endurance type work during the offseason is:
Rolling hill work- You find a really hilly area, this could be a park or a golf course, sprint the up hills and slow jog the down hills until you've put in 3-6 miles of volume.
150 on, 250 off. - Go to a track or measure a straight after your run. Run the 150s really hard, (3:55-4:10 mile pace for a 2:10 guy) and jog the 250 slow (for me that's about 8:00 pace). These need to be quality and shouldn't really have you struggling with pain, so if you feel you are losing the quality of the workout, add more recovery. Do 5-10 of these after your easy runs.
300s at mile pace, then walk 100. 4-6 of them.
These workouts never really hurt all that bad but they get you to good 800 fitness through the offseason.
Good luck!