Winning a race depends on your horse's attributes, its race readiness, and the features of the race track.
To prepare for a race, you can train your horse by using different exercises to increase specific attributes including Speed, Stamina, Start, Burst, Heart, and Temper.
Your horse's race readiness will depend on its Form, Rest, and Weight. Make sure all are at ideal levels before you race.
You can see the track features after pressing the race button. The description will be in the top box and include the terrain, furlongs and turn for the track.