Betting for most in game is just a side fancy.
To get up and running it is better to start a new game - don't buy any horses at the start of the season - have a look at the ones you have in your stable and sell the non performers.
Race the ones you keep and place them wisely and hopefully you can build your bank so you can buy a breeding barn.
Once you have that you can buy some cheapies (buy as many cheap fillies and mares without hurting you budget) and start breeding and selling to improve your bank again.
Don't worry about breeding quality yet - it's just about the cash.
Soon you should be able to start buying more expensive horses........then you can start putting them through the barn with an eye on racing them.
By this stage you'll start noticing patterns in the game where you can improve your chances on the punt and to bet here and there will be no drama.
Welcome to the game

PS betting on overseas horses in a local race has a handy strike rate.