When beginning stitching on a quilt, you'll want to pull out about 16-18 inches of thread. Any more thread, and you'll be spending more time untangling than you want. Thread the needle and begin by pushing the needle up through the backing fabric, and then slanting the needle just under the surface of the top fabric so the needle comes through at exactly the spot you want to begin quilting. When you pull the thread up through the top fabric, the knot will stop on the backing fabric. Give a tug while rubbing your finger on the knot, and the knot will snap up through the backing fabric into the batting, well hidden.
The quilting stitch should be one that you push the needle down through all layers, turn to the side only about 1/16 of an inch and bring the needle up through the top fabric.
Instead of taking a stitch straight down through layers and then (from the backing fabric) straight up through layers, take stitches only from the top....meaning the needle stays on top of the quilt stitching in an almost running-stitch fashion.



The idea is to make your stitches close together and even.
Having said that, keep in mind that the nature of quilting allows for some variation of stitch size. And only practice brings uniformity of quilting stitches. So just keep going!

Click the link below to watch The Quilting Stitch, from start to finish.

https://www.youtube.com/watch?v=Kewhr2FcN30&t=2s

Questions? Ask them in the YouTube comment section.