I haven't tried FMQ yet but I can so identify with the jaw-clenching activity! LOL

I just traced out what I wanted to do on scrap and followed them until I got the feel of it and took it from there.

Yeah, I do the same (jaw-clenching), but also tend to hold onto the handles of my long-arm with a death grip:)

As others have said practice practice practice. There is another class on Craftsy Ann Peterson. I can't remember the name, but she starts you right from the beginning and you finish a wall hanging when you are done. Here is my first piece with her. I had not done much fmq before. The only other I had done was Leah Day.

One day, you will get it. Just keep practicing. Some people learn quicker than others. But don't give up. Keep practicing on small things. You can also doodle the pattern you are trying to quilt on paper or a dry erase board. You will build a mental memory for it and it makes it alot easier to quilt. I bought a big dry erase board just for it. My mom bought a dvd to watch and it was by the pajama quilter. She is kinda fun to watch. I just spent time watching youtube videos.

I am trying FMQ for the first time also. The first try was really doomed from the go. As I keep working with it I can see I still need tons of practice. But my thrifty mind can't get around using all that fabric and thread just to dispose of so,,,, I made some into small bags and other projects using quilted fabric. I am practicing on wallets for My 3 DGDs living in Malawi, Central Africa... If the quilting isn't perfect they will still like the wallets!!

I am a self-taught quilter, and did OK with my machine quilting, but it wasn't until I took a class from Diane Gaudynski that I really learned what I should be doing, and I got so much more comfortable with FMQ after the class. Whether you take a class from a teacher in person, or on-line, I would encourage you to take a class somewhere. It does take a lot of practice though to get proficient at it.

Patti Thompson's youtube videos are good and there are some wonderful classes on craftsy. The nice thing about them is that you can go back and re-watch them. The rest is practice, practice, practice.

The class is called Beyond Basic Machine Quilting by Ann Peterson for Craftsy at craftsy.com. I have been fmq for years, but I am learning a lot from Ann! (I'm taking the class now.) I recommend it.

I agree with everyone else here...practice, practice, and practice some more!
If I had anything to add it would be to make sure you "press down firmly" with your hands while FMQ'ing as this gives you more control.

FYI, GLAD brand Press n Seal is amazing stuff! I would recommend that you use a marker that is similar in color to your chosen thread for the following idea, since I used a red permanent marker and could see a VERY faint...I repeat, VERY faint pink tint in a few places, so maybe use Crayola washable markers or something similar?

I printed out a motif I wanted to use, laid a clear cutting board from the dollar store over it, taped it down over the printed motif, then smoothed a piece of Glad Press n Seal over it and used a marker to trace the motif. Pull it off the cutting board and smooth it onto your block and stitch over it, then tear it off! I don't use this all the time, in fact I just recently used it for the first time on a quilt that was making me nuts. It works, AND it produces fantastic results! lol It also doesn't move until you pull it off, and you can do more than one block at a time and it's still in place no matter how much you move the quilt around.