I don't play the ponies, but my uncle does and I asked him what his system is since he does fairly well. Here it is in a nutshell.

1. Eliminate all horses not running back in 8 days or less.

2. From the remainder, eliminate the horses that didn't finish at least 3rd within one furlong of today's distance(as shown in their past performances).

3. From the remainder, eliminate all horses moving up or down 20% in class as measured by claiming value or purse value(stakes or allowance races)

4. If one of the remaining horses becomes the favourite bet it to place.

I don't understand what I just typed, but maybe it can help you horse guys.