I can only echo what the others are saying here when it comes to learning not only this piece but any piece that is completely new. All the advice is exactly what would encourage you to do. Here's how I go about learning a new arrangement:
• First, I listen to the arrangement numerous times before attempting to play it. This really gets the song into your ears and your head. As I recorded this in video form, do this with your eyes closed. After that, watch the video over and over again, to get a feel as to what I'm doing with my hands.
Even before I was fingerpicking arrangements, I was copying lead guitar solos as close as I could. I must have listened to these solos endlessly for weeks before I tried to figure them out. There were no books or videos back then, just the record. Consequently, once I did attempt the solos I could almost feel what the next should or shouldn't' be.
• Next, take a look at the tab to scope out the chords. Don't try to play it exactly yet, just get a feel for what your left hand should be doing. If there are any fingerings or chords that are new to you, now's the time to work them out... without trying to fingerpick. You're just concentrating on your fretting hand right now.
• The measure by measure system: This is a good way to approach the piece, but don't forget that once you have a couple of measures memorized, your next step is to CONNECT them slowly and seamlessly. Memorizing different parts without doing this will only trip you up when you try to put it all together.
• Like anything else, it takes persistence and patience. Don't try to do too much in one sitting. Smaller practice sessions during the day can be more productive than trying to squeeze everything in all at once. Every day is optimal, but sometimes that's impractical. However, everyone can usually find 10 minutes during their busiest day. Use that small amount of time to practice just the part of the piece that gives you the most trouble. This way, you're reminding your muscles what they just worked on the other day.
Keep at it. Remember that you're at the beginning stages of learning a technique that while wonderful, is definitely difficult to do at first.
At first is the operative term here, because once you get it, you'll never forget it and you'll be amazed at what you can start learning and playing at that point. It really is like learning how to ride a bicycle: once you get your balance and master that first turn, you'll wonder why you never were able to do this in the first place and you'll never forget it.
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