I learn a lot of songs, both lyrics and performance on other instruments. I've memorized 500-800, and I have a couple hundred tunes I routinely perform in front of people. Slow, perfect practice of component parts in all things is the only easy way to gain skills, IMO. Long-term periodic repetition is the easy way to keep skills. So, for instance, I can learn most generic country songs in about an hour. As with most…
If you're not already familiar with the term, it's "spaced repetition" - And is big in learning/memory.
Neither the "slow perfect practice" nor the "break down the skill" nor the "spaced repetition" is my invention.