I tend to cut down the races I play by mostly avoiding all maiden races (too much room for improvement that can't be calculated) ... I don't play much under 6f (one bad break and the race is over) or anything much over 1mile .... unless I can see something with a large advantage. I also avoid all BIG races ... love watching them .. but the bigger races tend to throw up bigger priced winners ... though class does tend to shine through in the bigger races.
I'm more of a short price/high win % player rather than looking for the 8-1 or 10-1 winner that will hit one time in 10.
Picking and choosing your spot and good money management is the key.