Just an idea to test out which seems to have gone well recently.

Using Racing and Sports Speed maps.

1. Only select horses which are Backmakers or Off Midfield.
Reason : These horse have the disadvantage in that they need to overtake the horses in front of them to win. Any holdup , interference or track bias could hurt their chances.

2. Only select horses in the $5 to $20 range on betfair (lay odds).
Reason: These horses are being seen at less then a 20% chance of winning, but the odds are not huge and/or overlays hopefully.

3. The horse must have raced at least 5 times already.
Reason: Can't have a speed map based on too few runs. You need a speed map that at least has had a few races to analyse the horses likely position.

Doing this I came up with the following:
27th July - 25 selections - 1 winner at $11
28th July - 15 selections - 0 winners
29th July - 12 selections - 0 winners (so far)

Over three days that is 52 selections - 1 winner for $11.

Might be worth following in the future.

Good Luck