Help me learn to "watch" a race

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Ok, I am going to keep this simple but I really would enjoy and appreciate some input. I have decided the past couple of days that I am going to employ a new method to my handicapping a days card. Since I have an online account that provides easy access to video archives of a horse's past races - why should I not take advantage of this feature? Which brings up this problem -

I don't know what I should be watching for besides the obvious. So, if any of you experienced players have the time and are inclined, would you please share a basic ABC elementary beginning to what I should start with?

Not only will it help me but all those others on this forum whom are not at that level. Thanks in advance!