What nativetexan said.
Some stencils are all straight lines - for those I use a walking foot. My machine has one built-in.
For curvy lines, I use the darning foot and do free-motion quilting (FMQ). Personally I do better with the feed dogs left up, but it seems to be something that really varies from person to person. FMQ isn't generally something you want to do for the first time on a quilt that's important; it's a good idea to practice on small quilt sandwiches made from scraps. Make yourself a bunch of potholders.
I learned a lot from watching Leah Day videos. She has hundreds of them - literally; she did a new stitch every day for a full year. She has an interesting blog too.