I am lead to believe that a tempo run is supposed to be about 10 secs a k over your 10k race pace. Can't remember whose theory this was or is.
My last 10k was a PB but that was in March last year. And that was at 3:46 per klm pace.
With that in mind I set out to do a tempo run at 3:56 per k pace.
Did a 10 min warmup and a 20 min cool down after finishing.
Ran 2.5k in 9:44. Average pace of 3:53 per klm. Close enough.