To handicap a horse race, start with the people Double Chance Dave involved. I know they call it horse racing, but it is really people racing horses. So first, look at the people who have the biggest impact on the races, I am talking about the jockeys of course. Each rider in the race will have a win average which tells you how often he or she manages to win. The better jockeys get the best horses and the best horses win more often so it becomes a cumulative process.
Good trainers don't put lousy riders on their horses, so you can figure that a good jockey is also usually riding for a competent trainer. If you want to check out the trainers you can find statistics for their winning average as well, but just looking at the jockeys in the race and their win averages will probably be enough to get you started. You will find that at most race tracks, a handful of jockeys win the most races while the second rate riders will pick up a win here and there, usually in the lower classes of races.
So go through your racing program and find the top three jockeys in each race based on win percentage. Some racing forms and programs now also give a winning average for the jockey when he or she is teamed up with that particular trainer. That is another very important statistic because successful jockey trainer teams account for most of the wins. Stick with the top three jockeys in the race and you will have a much better chance of winning.