Tempo runs are sustained 20- to 30-minute efforts (about 2 to 4 miles in length) done at 10 to 20 seconds per mile slower than your current 10K race pace. You can do tempo runs on any measured, flat road or trail with little traffic and safe footing.
By the end of a tempo run you should feel taxed, but not wasted. One common mistake runners make in tempo training is to run these sessions as all-out speedwork. Don't do this. The greatest gains from tempo training occur when you have the discipline to stick with the slower-than-race-pace plan.
A combination of tempo runs, easy recovery days, and a weekly long run of 8 to 12 miles should bring down your 10K times.
As your 10K goes from 50 minutes (8:03-mile pace) to 48 minutes (7:42-mile pace) to 46 minutes (7:23-mile pace), adjust your tempo pace accordingly.
For example, at the 50-minute 10K level, your tempo pace should be around 8:20 per mile. At the 48-minute level, the tempo pace should be around 7:55 per mile.