If you look at the horse's past history of races and which distances it has done best at, you can work out if it will keep the pace up. Then you just have to match the horse's performance to what's known about the course. I had my best win on a horse with rather poor odds (33/1) that was described as "Slow, but a stayer" on a long race with a large field, when it had been pouring with rain the day before. It seems I was the one of the few who noticed that every horse with shorter odds liked dry going.