if you did suddenly have a track in your backyard but hadn't done an interval (other than the 400 m from the GO control to the Finish box) in ~20 years, what would you start with? One mile warmup then easy 400s at 5 km pace? Slightly warmed up miles with a little break in between?
I wouldn't actually run on the track unless you had an event you were considering in 8-10 weeks.
Assuming that's the case (and its a 5k) then first you need to get your legs ready for faster running. 2 weeks of Fartlek 2x a week over various distances during your regular runs.
Then, assuming you know what your VDot number is I'd start with 2-3 1200m repeats (whatever distance takes you 4-5 minutes) at 5k race pace (not your goal 5k pace but whatever pace you ran in a recent 5k) once a week and 2-3 1600m repeats at your threshold pace with 1 minute rest in between on another day of the week. This would be done for the next 2-3 weeks.
The last 2-3 weeks I'd replace the 1200m repeats with 4-6 400m repeats at R and continue with the threshold workout as earlier (on a different day).
1 week before your race I'd skip the threshold workout and replace the 400m repeats with (6) 100m strides. Strides are just drills focusing on good form, typically a little faster than 5k pace. All speed workouts have a 10 min wu and cd.
Race day- 1st mile should feel easy but exactly on the pace you need for your PR, 2nd mile you should feel like you're constantly increasing your pace but end result is again you're right on your PR race pace, 3rd mile is sheer agony, you can't wait to cross the finish line to make the pain stop. End result- PR.