I'm extremely OCD when it comes to watering - probably to the point of overkill. I use a Blumat Digital tensiometer (available on Amazon for around ) to determine soil moisture levels. I have found the Blumat sensor to be to be quite accurate. I then use the soil moisture numbers provided by the Blumat to determine what watering schedule I want to be on - once they're past the seedling stage I like to water every other day. In addition to the Blumat, I keep a digital scale in my grow room and I actually weigh my plants daily. Between the Blumat and the scale I've been able to really dial in my watering. For example, at their current stage of growth, in 5 gallon buckets using Fox Farms Coco Loco soil I water my plants every 2 days to a weight of 24 pounds. Typically, after 2 days have passed their weight will have dropped to around 18 pounds, so I water them back up to 24. The Blumat tells me if the weight range is providing enough water to ensure the soil is always adequately moist. Doing all this keeps my plants on a consistent 2 day cycle where they go from being slightly overwatered to slightly under-watered. Of course, over time as the plants grow and are transpiring more water, the upper weight value needs to be raised - the Blumat lets me know when the upper number in the weight range has become too dry and needs to be increased. As needed, I just increase my upper weight/watering by amount by 1 pound (which equals 1 pint of water).
For me this method has proven to be foolproof.
Did I mention I suffer from Obsessive Compulsive Disorder! LOL
Good luck with your grow!