Thanks for the example!
I have a few things to offer here.
First - whenever you are trying to play a piece that has a challenging passage - those 1/16th note phrases - make sure of the following:
1.) That you can sing the fast part perfectly. This is so that your musical brain and your ears know exactly where the notes are, and exactly what they sound like. If your ears (music brain) can’t hear and make sense of the phrase, it means you’re asking your eyes and hands to do all the work, and they have a very hard time executing confident musical ideas if the musical brain and ears aren’t leading the charge.
2.) Try different fingerings if possible. That open G string in the 2nd bar seems very suspicious to me. I would be playing it on the 5th fret of the D string. It would make a much nicer fingering (in my opinion) for that quick batch of 1/16ths
3.) Play the challenging part slowly slowly slowly slowly slowly. Don’t play it faster than you can execute it 100% perfectly. Just roll through beats 3 and 4 of bar 2, and land on that first note of bar 3 until it is smooth and easy and perfect at a nice, slow tempo. Then go up a few clicks. Do this until you have it at tempo. If you can’t get it at tempo, then set the piece in the “save it for later” pile, and keep on the technique and fingering exercises to build up coordination and speed.
1 - get it in your musical brain and in your ear
2 - check for best fingering options / alternate fingering options
3 - play it slow, over and over, speed it up gradually.
That’s the advice for a piece that has challenging bits. There are totally different hurdles to jump over when the song is monotonous and simple. If you come across that and find it challenging, again, throw an example up and folks can chime in.
Best of luck!