Strides, much like intervals and tempo workouts are always left up to interpretation. I would guess that if you polled the top ten coaches on anyone's list, they would give you 10 similar but different answers.
However, the intent should be the same for all variations: Strides should allow you to spend time at a faster pace than what you would normally race at.
Most advice that I follow talks about strides as one of the few ways that distance runners can improve/maintain overall running speed.
That's not to say that you should run them as hard as you can, just that they should be much closer to your top speed than most normal runs.
From a practical standpoint, I abide by the following rules:
1. Never run farther than 100 meters
2. Pick out fire hydrants or telephone poles or some other landmark to focus on
3. Don't spend too much time worrying about form. You'll get 10 different answers on proper form also. Doing strides over time will improve your form all by itself. You don't need to "fix" anything
4. Strides are faster than 5K pace and aren't all out. Let your body dictate how fast it wants to run.
5. Don't get too aggressive with strides. They are supplemental pieces to a complete workout plan. If you want to show how tough you are, do it at a race or a hard workout.
6. If you don't have time to do them at the end of a workout, just work in short bursts during the last half of an easy run. Same concept.
The key here is that you are giving your body an opportunity to run at speeds faster than it normally runs in a way that will not impact your normal routine.
Hope this helps,
The Wagon