First, lay the right side of the backing on the carpet and smooth out any wrinkles. Remember, backing and batting should be bigger than quilt top, at least 2-3" on every side. Once smoothed out, start pinning around the perimeter to keep it in place, every 8 - 10".
Once the backing is secured, layer on the batting.
Next layer on quilt top, right side facing up and start pinning.
I use curved safety pins. I think they work best whether pinning on hard floor or carpet.
I was taught to pin from the center out, which I did for a long time, but now I pin from one end to the other. Also, I used to pin about a closed hands width apart (4"), now I pin about an open hand width apart (8").
So this is how I baste my quilts. Occasionally I do pin to the carpet, but surprisingly it doesn't happen often.
A Thread for Life
May the grace of the Lord Jesus Christ, and the love of God, and the fellowship of the Holy Spirit be with you all. 2 Cor 13:14