I guess we all have our favourite filters. How about:
-for 1400m + races, no more than 21 days since last run.
-all races, barrier no worse than 11.

Win percentage is a funny one. When you do your analysis, see if lower win % gives better value, especially in the more competitive races on the card - the last two or three races usually. Not sure why lower win % is a positive - perhaps lower win % horses got to this class with fewer close finishes, therefore less wear and tear on their bodies. Or perhaps they are closers, which get up less often, but are better value when they do.

Hope that makes some sense.