I would suggest the opposite of whatever the normal racing mythology proposes...
i.e. maidens - Yes! 100%. Maidens are a lot easier to bet on for a number of reasons. Generally smaller fields, often only a few runners have ever run a race before. It is my humble belief that most people, if they put their mind to it, would have a better success rate in betting on maidens than your average BM70 race.

Ignore "great races" unless they are a sprint with someone like Winx in it. The more "good" horses in a field, the harder to pick who will win.

Only bet on the first 4 races on the card. In most of the systems I have tested you are better off betting on the 1st 4 races. Not always true, but generally true. Similarly, I find it is generally more successful to bet on day time races for both racing and harness.

And the all time mother load of race selection methods - stop when you are ahead!

Oh, and always pick the fastest horse in the race :-) (this means if you cant identify a horse that is obviously faster than the others, dont bet that race.)

Have a great day....
ET