practicando para poder tocar o ejecutar la guitarra
I think that Spanish speakers don't translate directly that they are practicing an instrument, but rather say that they are practicing to be able to play an instrument. However, if we go strictly by the correct term used in music. The word "ejecutar" is more appropriate than "tocar" when saying "to play the guitar". Therefore, we would say "ejecutar la guitarra". Here we have "practicing the guitar" so the translation above should fit depending on how formal is the surrounding context of this phrase, since you can pick between "practicando para poder tocar la guitarra" (informal) or from "practicando para ejecutar la guitarra".