Best system is

1) Discard horses who won last start
2) Discard horses coming off a spell
3) Horse must be in top 5 newspaper ratings
4) Horse must be top 5 in betting.
5) Horse must be $15 or less in newspaper betting
6) Horse must not have a weight shift of +3kg or -3kg or more from last start
7) Horse must of placed at distance and track before