First, make sure your backing & top are pressed nice & smooth. Then what I do is this: put the backing down on my table right side down, & fasten (either clamps or duct tape) it to the table, making sure it is as smooth as possible, & taut, but not too tightly fixed down. Next l put down the batting, and smooth it too. Last, the quilt top, right side UP, and smooth, smooth, smooth! Then I pin baste, using the curved quilter's safety pins, starting in the center & working my way to the outside. I DO NOT close the pins, but leave them open (& I try not to stab myself with them too much! lol). After I have all the pins in place, I carefully take off the tape or clamps & turn over the sandwich. If it is all smooth with no puckers, then I turn it back over & close all the pins. If there is any place with a fold or pucker, I usually only have to remove a few of the pins to fix it, and then when it's OK...close the pins.
Hope this helps! I know there are many other ways, but this one works for me.
sue