I get asked this ALL the time - How do I not get the pleating with all the grid quilting I do???????
Well, ask and ye shall receive!
Safety pins. And lots of 'em. It's how I baste ALL my quilts. I've never spray basted because I've heard it's one of the big reasons quilters get pleats.
Another tip - As I'm quilting, I pull the fabric on either side of where I'm stitching really tight, all the way up to and through the machine, and I keep doing it until I get to the end of a line. It helps A LOT.
A walking foot is a big thing too. A walking foot pulls the top and bottom fabrics at the same rate, so you get no pleats or puckering. Well worth the investment if you are serious about any kind of sewing or quilting.
I know there are some quilters who swear by spray basting, or what have you. To each their own :).