According to Mr Galloway, the "Magic Mile" time trials (MM) are reality checks on your goal. These should be done on the weeks noted on the schedule. The MM has been the best predictor of current potential and helps us set a realistic training pace. With this information, you can decide how hard to run during various situations. (If you have any injuries you should not do the MM)
Warm up for a Magic Mile with about 10 minutes of very easy running with liberal walk breaks
Do 4-6 accelerations. No sprinting, just gradually pick up the pace of each 40 to 50 meter segment to about what you want to run in the MM.
Run around a track if at all possible (or a very accurately measured segment)
Time yourself for 4 laps (1600meters). Start the watch at the beginning, and keep it running until you cross the finish of the 4th lap.
On the first MM, don't run all-out: run at a pace that is only slightly faster than your current pace.
Only one MM is done on each day it is assigned
On each successive MM (usually 3 weeks later), your mission is to beat the previous best time.
Don't ever push so much that you hurt your feet, knees, etc.
Jog slowly for the rest of the distance assigned on that day taking as many walk breaks as you wish.
After you have run 3 of these (not at one time--on different weekends) you'll see progress and will run them hard enough so that you are huffing and puffing during the second half. For prediction purposes, you want to finish, feeling like you couldn't go much further at that pace.
Try walking for about 10-15 seconds after each lap during the MM. Some runners record a faster time when taking short breaks, and some go faster when running continuously. Do what works for you on the MM.