There's a difference between learning to play an instrument from a printed page and learning music. It's like operating a typewriter.
I know a lady who is very efficient on a typewriter keyboard, and can type circles around me as long as she has some sort of copy to work from. But when she wants to produce something original, such as a personal letter, she has to write it down in longhand first and then type it.
My typing skills aren't the greatest, but I am a writer. A typewriter or computer keyboard is an extension of my brain. My creative thoughts flow from my brain to the keyboard.
Much of so-called music education is aimed at teaching the student to transcribe the notes from a printed page to a specific instrument. A person can become fairly proficient at doing this and impress audiences, but this is only a tiny part of learning music.
Music is learned first by listening to it. And whether or not you like the music you hear has a bearing on what you will learn from listening. A student taking formal lessons will be exposed to a limited selection of music. First and foremost, it will be music on which there is no copyright. The authors of the textbooks will copyright their own arrangements of the tunes, but they don't have to pay royalties. This, of course, eliminates current popular music.
The music teaching establishment goes even farther to keep students from learning to like music. Teachers and often parents will actively discourage students from listening to current popular music. They say it is not good music, and only classical music which has stood the test of time is good.
Here is where the old folks are wrong. Classical music is popular music from centuries gone by. Much of it was considered vulgar when it was first performed. The waltz was once banned because it might incite persons to do indecent things. The theater was once thought to be vulgar, but today's dowagers feel very dignified in attending productions which might have been banned a few centuries ago. The pop tunes from 50 years ago are cherished today.
Really there is no objective way to define which music is good and which is bad. As long as a piece of music makes someone feel good, it is good music. The only thing that matters is audience satisfaction. If music can find an audience, it's good. The bigger its audience, the better it is.
So in learning music, a person should listen to whatever suits his or her fancy. If you want to learn an art, it's good to first study the existing art.
People who listen to music a lot will memorize tunes so they can hum, whistle or sing them. This comes naturally to a person with talent. The simple tunes are the best, particularly with a good swing or strong beat.
Much popular music plays the notes of the major triad, Do-Mi-So, with more emphasis than the other notes. On a harmonica, these are the exhale notes. On a diatonic accordion, they are the push notes. The inhale or pull notes generally get less emphasis. This makes a diatonic instrument feel natural to play. A person who is musically inclined can learn to play tunes on a harmonica just by fumbling around with it, as long as the tunes are in the person's head.
The nice thing about a harmonica as a beginner's instrument is that it's not expensive. Almost any brand of harmonica is a good starter, and inexpensive brands are not hard to find. Often they are sold in blister packs in novelty stores. A Hohner harmonica may cost four or five times the price of a cheap brand, but it still costs far less than most instruments and is sold by many music stores.
A harmonica is a natural-feeling instrument. About the only thing more natural would be a kazoo, but it only changes the character of sound made by one's voice. The harmonica relates directly, on a note-for-note basis, to a button accordion.
When I was a youngster, I often listened on the radio to a daytime polka station. Its theme song was the Tinker Polka. Before long I was whistling the Tinker Polka. Later, when I started with the harmonica, it was one of the first tunes I learned to play. It took a little longer to learn Home on the Range.
For people learning to play from the printed page, there's a good way to supplement their lessons with more familiar material. Some music stores have sheet music in an easy piano version. But just because it says piano on the front doesn't mean it can't be played by other instruments. An accordion, fiddle or other melody instrument can follow the melody line.
There's really no secret to learning music. Just listen to and enjoy the tunes you like. Sing, hum and whistle.
Before we close this, we need to look at the logic in the brain when playing music. If you already have the tune in your head, you need only train your fingers to find the note on the instrument and play it. You don't think about where it is. The brain bypasses the thinking process and gives a direct order to the body.
When a person starts to read music and play it on an instrument, the brain has more work to do. First the brain must recognize the note. Then it must locate the note on the instrument and command the fingers to play the note. Finally, after all this, the brain hears the note through the ears. This is not an efficient way to operate, but many would-be musicians never get past this stage.
The better way to do it is for the brain to see the note on the page, hear the note in its own memory and, knowing where the note lies on the instrument, command the fingers to play it. The brain should do this without thinking. It's like when we sing or hum, we don't think about the mechanism that produces the sound at the desired pitch. This comes quickly for some people, slowly for many and never for the rest.
Either way a person goes about learning music, the goal should be to play it without much concious thinking. This takes much practice, but it comes faster when you play music that touches your heart.