Don't spray neem on buds. Spray at lights out or sundown. If strong light is on leaves wet with neem spray, they will burn badly.
Use the instructions on the bottle. I use Neem Bliss Neem 1oz/gal with 1tsp/gal Dawn concentrated dish soap as surfactant/emulsifier. Be sure to mix very well. I use a mixing attachment on a high speed drill to mix, but that's not necesarry for small batches. Just mix/shake very well.
Treated every 1 to 2 weeks all the way through veg with full strength neem, bt, and spinosad with Dawn concentrated dish soap as emulsifier. Seems to work fine for me.