Hi!
There's a lot of different ways to incorporate speed work into your runs. For example, here's this week's speed workout:
1 mile w/up
14 laps running hard on the straight aways and jog the corners
2 / 200 s hard 200 recovery
1 mile cool down
I like this because it's individual. In a group "running hard" will be interpreted to mean different things by every individual.
Or a 1 mile warm up. Then do 12/400 m with a two minute recovery after each 400m. Finish with a 1 mile cool down.
Another "laid back" route to speed work is to run with your Ipod of music maker of choice, running much faster for half or a full song, then pulling back for the next song.
Or "cresting" which consists of running hard on the uphills until you're over the crest of the hill, then slowing down for the downhill and the recovery. The idea of this is to push hard and push past where one would normally stop or slow down, until past the crest of the hill.
Hope this helps.
Bean