Memorization is not so much developing your "memory" but more like using "mind tricks."

First, and foremost, learn your "cycle of fifths" and you'll learn more than half of your songs overnight.

Practice simple songs in different keys until you get used to hearing the "chord changes" in your head. Example: Five, Foot, Two...All of Me...You're Nobody, etc. They move in "fifths" and in both songs the first measure root chord moves to the third (E7). This happens in many songs before the cycle of fifths kicks in. Also, the interval C to A7...a very important jump. It doesn't take long to recognize that change in many songs. Example: Ja-da, So What's New, etc. All accordionists are a step ahead on this as the left hand buttons move in fifths.

I have success with the following. Take a "stack" of songs you want to learn and put them in groups of 5. Go over one group until you've memorized the songs maybe 50-75%. Put that group to the side and start on the next group and do the same thing. When you've finished ALL the groups, start again with the first group, and learn each one maybe 75-85% (it will be easier this time around). Keep going through the cycles until "it comes easy" with each song.

It will, as that's the way the mind works. NOT by memorizing in one sitting but by steps with breaks in between. I've memorized hundreds of songs with these techniques, plus other "tricks" I've had to discover.

Lucky