In my case, practice, knowing the course, and running close to my easy pace all help. I have a pretty good sense of what different paces feel like, effort wise.

In my case, practice, knowing the course, and running close to my easy pace all help. I have a pretty good sense of what different paces feel like, effort wise. But I also use a GPS watch and Stryd pod to monitor my pace in real-time and keep track of my 1 mile and 5K splits. Generally though, runners tend to go out way too fast in a race because they are very excited and should have gone through a taper, so it feels easy while running too fast at the start. Because it's not a race for me, I can avoid that excitement. Then toward the end, they slow down because they went out too fast. Since the entire race is at a relaxed effort for me, I can avoid that too. I also probably haven't spent the last 10 days tapering, so I don't have to really adjust my feel. That said: a few years back I ended up pacing the 4:30 marathon group which was almost 3 minutes/mile below my race pace and I was constantly having to check myself. My preference when pacing is to be close to my easy pace for the distance, not to fast, not too slow.