I think Judy Garland said, "If you can't remember the lyrics, you need to study the words, and get into the head of the composer, focusing on his/her motivation to write the words in the first place.
She also said, which I used in a Shakespeare class, that if you break up something into small chunks, then go to different parts of the house (admitting it's easier in a very large house with lots of rooms) and picture in your mind, THE ROOM and a KEY WORD in the first line.
Actually in acting, it would be a key word in the lead-in line.
When singing, then, you'd mentally move from room to room, or place to place, singing one verse in each space.
I did it with MacBeth (that wonderful speech when he's told the queen is dead) and it helped. I recall it like yesterday, the lead-in, "The Queen, me lord, is dead". To which the ol' guy replies, "She should have died hereafter. . .(ol' Willy Wigglestick wrote great stuff).