Neem is an oil, so you need to emulsify it in water (since you use so little of the oil in a quart sprayer.) Soap is dish washing soap, the liquid squirt bottle kind, and you only need like half to a tsp per quart. It only breaks the oil up evenly into the water, so the amount isn't critical. The oil is doing the bug-killing work.
I spray as my pests suggest. I have few problems, but that's because I grow indoors. Outside, you're subject to the world! eeeh gads! If I have a plant with more than an occasional scale, I'll spray preventitively: every 4-5 days. That will catch any hatching babies you might have missed in the first pass. I only need to do that once or twice to get everything.
But I'm inside in New England. Outdoor growers will have a stricter regime, I'm sure, and warmer climes will invite more beasties.