The only way to win at betting is to find 'value.' For example, let's say Andy can find value in certain horse races. After much studying of the form
and a few jars of Guinness, he finds a horse that has a 6-4 chance according to his 'expert' judgement. In the bookies, the horse is rated at 5-2 odds. Now if Andy's expert analysis is correct, he has found a 'value bet', which over the long term would yield a positive expected return of 140% gross. That is how professional gamblers win at betting. They find 'value bets', and then only bet at level stakes they can afford, never increasing their stakes or chasing losses by backing horses that offer poor value.
The problem with horse racing is that one needs to be an expert in studying form to find any value because of the over round. I don't understand horse racing myself and so don't bother with it. I play poker instead which is a game of skill.