This is what I did there are other methods.
First I steam cleaned my floor to make sure it was not going to leave any marks on my fabrics. Second I layed down my ironed quilt back making sure it was wrinkle free, I had run out of masking tape so I used some low tack tape instead just to hold it in place.
Centre the quilt top on the wadding right side up smoothing as you, keeping it straight and centered.
Starting in the centre of the quilt using basting pins I curved saftey pins) basted the 3 layers together.
Thats it. Don't try to rush the process just work away methodically. Now you are ready to quilt.
Hope that has been helpful.