Never actually tried P before, just went straight to manual and learned from my mistakes (about 3000 photos seem do to the trick)
Just for my knowledge though, P basically works out the shutter speed/aperture based on exposure bias? Although it seems you can adjust the aperture too and ISO? *seems even more confusing than manual*
Most important thing i ever learnt was the minimum shutter speed require to avoid shake for each focal length (roughly 1.6 (crop factor) x the focal length) once that was set, i'd adjust the aperture depending on the situation. Although i generally shoot wide open with f1.4 primes then i usually leave ISO on auto since i've capped it to 1600 in the settings anyway.