write down the words. It alters the ways your memory registers. Adds to it.

The way I always explain it is the analogy of a stool.

one legged is a shooting stick, not very stable unless you put two feet on the ground see below. Two-legged stools are not that popular, but a three legged stool is optimal (see shooting stick). A 4 legged stool is prone to minor changes depending on terrain.

So - learn the words by repeating them. Writing them down & singing them regularly in the bath, or car. Ergo - three routes. But don't rely on the security blanket of a song sheet - to mix a metaphor.