For years I loved doing free motion machine embroidery, especially before the embroidery machine made embroidery so easy. At that point I sharpened my skills on free motion quilting. Both skills were creative and I found them relaxing once I got my machine to work smoothly. One product that really helped was to use of an open toe foot free motion foot. There are not many accessory feet produced but I have found a few that give great visibility and are easy to use. Singer has some free video on how the free motion foot is used. Stippling is the term used to describe the free motion technique using small meandering S shapes to quilt the background area in a quilt.
Free motion embroidery can be shown with many different technique. My favorite is a technique by Terry White. Here are some links to her video and products showing free motion embroidery. Any straight stitch machine can do free motion embroidery. Time and practice develop the skill.
The first thing to do is know what kind of shank your sewing machine has. Most machines are low shank, slant shank, or high shank. Before you purchase a foot for your machine tell the merchant your machine make and model. That way you are sure to buy the correct shank for your machine.
Juki has a great low shank open toe free motion foot with adjustable pressure that makes embroidery and quilting easier. If you do not own a Juki, I have a generic open toe free motion foot that will fit most low shank machines. My personal favorite is the rocker foot for the low shank machine and is made for Singer.
One final idea for free motion work is to have a flat wide sewing surface. Some machines have optional slide on tables you can purchase to make the quilting and embroidery much easier. I also offer a generic table and custom cut tables called sew steady tables. Take a look. These tables are well worth the price for the support and extension they give.