Realistically, break it down into its sections, and then create a road map in your mind. But before that, know and understand the various basic building blocks of the modern song…intro, verse, pre-chorus, chorus, bridge(AKA “middle eight”*)and/or instrumental break, turnarounds, coda, and so on… then realize that there’s no uniform combination of these elements, it changes from song to song. Mentally, I liken it to driving around the block, over and over, with occasional stops at various places across the street, perhaps only once.
Generally, though(and it’s not a hard and fast rule, there are always exceptions), beyond the intro(if there is one), there’s a verse, maybe a pre-chorus or build-up, then the chorus(of course), repeat the cycle, but then…it’s kind of a psychological thing, but to keep it from being repetitious and boring, you take it elsewhere. To a bridge, a related but separate “aside” which serves as a momentary diversion from the V/C.
After that you might follow with an instrumental break, usually over the verse and or chorus chords or maybe even the intro, sometimes the intro can serve as the bridge, then… maybe repeat the bridge, or else just go straight to a third verse(and chorus), or just the chorus, finish up, and you’re done. A coda is basically a separate “grand finale”, but you don’t hear that too often. On the other hand, there are some songs that are just V/C over and over that aren’t monotonous, but usually those are kept to three cycles.
Think of a tune in terms of a flow chart or maybe building blocks, and it won’t be so overwhelming. List some the songs you’re working on or are favorites, and I’ll try to break them down for you.
*middle eight is a quaint term referring to that section, separate from verse and chorus, that was usually only eight bars long in the old days, but a bridge can go as long(or short)as it aesthetically needs to be.