This may be completely contrary to what most coaches subscribe to, but this always worked for us when I ran and this has always worked for me as I started my coaching career.
For mid distance runners we workout almost completely on the track. This may cause some problems with shin splints for some runners so we will also do a lot of our work on the grass.
Mondays will be 200's. Start the season with doing 3-4 sets of 4 200's @ 30-32 secons. Rest is 30-45 seconds between 200's (we start around 40 and rest gets less and less as the season progresses) with full rest between sets (heart rate down under 130 is considered full rest).
Tuesdays will be 400's. I have several 400 workouts. You can be plain jane and do 400's @ race pace (we will train for 2:00 halfs so 60 seconds will be our goal repeat pace). When we do this we will do 6-8 repeats. Another good 400 workout is run 1 400 @ 80-85% of race pace (68-72 seconds), wait one minute, do another at same pace. 3-4 sets of this is more than enough. I have others if you want them just let me know.
Wednesdays will be our recovery day. Often this is a short run 2-4 miles but more often will be active recovery with maybe a fartlek run or even a pool workout. This is up to you. I hate running miles for running miles sake becasue it promotes slow twitch muscles growth and to me is counter productive.
Thursday will be our last tough day. Usually 300's or 600/200 combo's or a ladder workout. 300's will either be simple repeats (38-45 seconds with varying rest), or active recovery again (300 repeat, jog 100, another 300, repeat until run 4 repeats) x 3 sets. The 600/200 workout consists of running a 600 @ race pace (1:25-1:30), rest 30 seconds, sprint a 200. This mimics running the half and helps develop a kick. Our ladder workouts are pretty typical. 100, 200, 300, 400, 400, 300, 200, 100. 2, 4, 6, 8, 6, 4, 2. Or maybe a 3, 4, 5, 6, 5, 4, 3. Be creative.
This is just the tip of the iceburg. Like I said these worked for me. Obviously these are all mid-distance workouts. Tweak them for the milers. Increase number, decrease speed for the 2 milers. I'd love to hear everyone's take on all this. Good luck to all and looking forward to a great track season.