I'm new, too, and you'll probably find as many answers as there are players. That said, concentration is something you can expand with practice. You may also find that talking to yourself in your head is counterproductive as you can interrupt yourself in process and make a hash of things. We are also very different on different days, so anything like disc golf is a way to check yourself and see where you are at in the moment.
One of the biggest reasons I play is to force myself out of my head and into my body. There are a few things that have helped me increase my concentration, stop my internal monologue, and be more consistent day to day. One of those is the board game GO. It requires total concentration. I'm not good at it, but playing consistently has increased my ability to concentrate over longer periods. Another is the concept of Mantra like so many Eastern religions practice, which put simply is creating a sound or chant that you can repeat that overrides the language in your head. It's like giving a dog a bone to chew on. Your body is then free of being pestered by your head. On top of this, being somewhat purposeful about breathing is obviously a way to center yourself.
In addition to this, nutrition and hydration really can goof up your head. If you are dehydrated your head will be more jittery.
Not all of these are "on the course", but they influence me on the course. I tend to be verbal in my own head about disc choice and my shot shapes, but then I turn the language off and try and execute without interrupting myself. It's the recursive mind—the second guessing while in motion—that is a killer. You'll hear people say "I didn't commit to that shot". I think part of that is second guessing the shot in mid stream.
On top of all this, simply getting outside more always helps. The more you can be outside the better you'll do. I spent much of my 20s and 30s backpacking in small groups. There's something that happens on about the third day of walking where your nervous energy is gone and everyone syncs up and starts functioning better. Your feet get more sure and confident. You are more comfortable just breathing and being.
I always appreciate playing disc golf with someone who is not constantly chattering. I play by myself most of the time, lol
I've also heard people say, in terms of form, to work on one thing at a time, or not too many things. I think that's gold. Let yourself not care about everything and focus on one thing and let the score ride. It's all about neuroburn and allowing you body to get the feel of doing something right. If you get a good shot off, stop and remember how it felt and rerun that a few times after the round. Your body is smarter than your words. It's faster and can do more. Words jam it up.
