Practice, practice, practice. And if you're getting tired of hearing that, try practice, persistence, and patience. Drawing and doodling sesigns works wonders for improving FMQ. Not just muscle memory, but also learning how to get into and out of tight quilting spots. Gloves or some other grippy method is essential, as is having a good, flat, smooth surface to quilt on.
To keep from wasting too much fabric and batting in the early stages, try using a fairly tight woven fabric for the quilt sandwich and a large needle, but NO thread! You should still see the path of needle holes enough to get a feel for what you are doing. A quick press will remove the holes and you can start over.
Leah Day as others have mentioned has great ideas for fillers, increase the scale when first starting out. Everybody has their own style too, find what works for you. Designs based on the piecing is marker friendly and less random than fillers, so you know where you're going. Choose designs that have good places to stop. I don't consider the regular stipple to be a good design to learn on because it is so random and doesn't have good places to stop and reposition your hands.
Frankly, I think my stipple looks like crud, but I can feather all day long.....
There are a lot of great sites out there and videos on youtube too. There's always something new to learn! I have tips and such on my blog, but I guess I'm not supposed to link to it here as that's considered self-promotional.....