Never let your plants drown or drought. Slightly moist soil is your best bet. If the ground is saturated, the plants will rot at the roots. Not enough water will cause dessication. In the heat of summer, especially, keep an eye on the plants. The curling and drooping of branches and leaves is an urgent indicator: Water!
Watering in the morning or in the evening ensures that the most amount of moisture is reaching the plant and not just evaporating.