The general rule is to arrive at the track half an hour before the start of the first race. This should give you enough time to park your car - should you chose to arrive with your own transport -, find a good spot for the first race and get a start on the betting. Most race tracks offer free parking to ticket holders but it is adviseable to check online or over the phone to avoid unpleasant surprises. For major events you may have to book your parking spot in advance to steer clear of complications.
Also, you would be well advised to check whether any special activities are planned before or after the races. Race courses frequently offer live music, children's entertainment, or show riding feats before a race; features that it would be a shame to miss out on.
Some race courses offer a shuttle service from the venue to the nearest train station, which is included in the price of your ticket. This is an excellent way of enjoying a race day without worries about traffic, drink driving and the tedious way home. Again, be sure to check whether this is the case and whether you have to be ready to leave at a certain time in order to make use of this service.