Tailwag, if you look for obvious things "like the obvious weight, latest form and so on", you are wasting your time. It is all there for you free, reflected by the odds, tipsters polls etc.
To find that elusive angle, you have to look outside the square.
I worked long and hard on my original rating only to find, that I was getting the same horses almost in the same order as everyone else, so I stopped using it.
Now for the last 4 or so years I've been using a different method altogether AND making profit. All I am prepared to disclose is, look at the reason, why some horses are shunned by punters?
Once you selected those, you can still put them through a proper rating to sort them in ranking order.
Good luck!