i taught myself how to play piano. and yes, it's much easier if you know how to play another instrument. I know how to play the violin, so I know how to read music, however, im weaker in the bass clef because violin reads only the treble. however, i adapted quite quickly to reading bass clef by knowing the relationship between bass clef and treble. Learning where each key was on the piano was easy also, because once you know the location of one note you can figure out the others and as you play more, those locations will eventually lock into your memory. The only thing i'm missing from piano is technique. Fingerings, positions, form, etc. Things that trip me up when im practicing is rythm. Sometimes, theres a weird rythm in the left hand and right hand is doing somthing else. Similar to playing drums, where each one of your hands and feet are doing something different. my brain has to adjust, for trained pianists i'm sure that's not a problem, but for me i have to play it a dozen times to get it. Currently, i've taught myself to play Joe Hisaishi's "Ashitaka and San" and i'm working on a solo piano piece that i think is more difficult than i can play.