teaching yourself a song on the piano?

Okay, I’m teaching myself how to play it ends tonight by the All American Rejects on the piano. I quit lessons last year but I took for about 5 years however I never got that good. I’m trying to teach myself the 6 page moderately hard song, and the timing and stuff is screwing me up, so any tips for learning how to play songs on the piano and teaching it to yourself (like how much time should I spend on one bar, how should I split it up, etc.) thanks!!

start out slow and work in sections, slowly building