I use the thinest needle and thread that my machine likes. Since the needle is making a ton of holes in the background fabric, I like them to be as tiny as possible. I use a stabilizer behind my background fabric to prevent tunneling and so the background fabric doesn't get all wrinkly. If you are layering pieces, do the satin stitching on the pieces that are behind others first. I like to leave my thread ends long so I can bring them to the back of the background fabric and knot them before trimming. Watch a video on going around corners and curves to see which side of the zig zag you need to be on with your needle to reposition the background fabric so you don't get any gaps. If you have needle down function, it really helps.