Water until runoff and let flats dry out between watering. Beware of high pH in the water. We killed a ton of stuff due to this. We now adjust our water pH to 5.6-6.0 by injecting battery acid directly into the irrigation water along with the fertilizer. PH induced iron chlorosis is an insidious problem.
Plants weakened by it quickly fall victim to fungus gnats and aphids.
Properly dry flats will be flattened when you water but show little sign of wilting before the water hits them, and will recover quickly with no tip burn. There are many formulas for success, but the most important ingredient is patience. The only thing to do with some species is to sow and wait for a couple of years. Many seeds will germinate immediately with the majority coming up a year or more later. Often the early germinators turn out to be the weakest plants.