I recommend laying the biggest flat sheet you have over the table first (or possibly on the floor, depending on how big your table is and how big the quilt is) to catch overspray. Just toss it in the laundry afterwards. This is a lot easier than scrubbing a floor!
What I do is first smooth out the backing. Then I smooth the batting on top of the backing until I am satisfied that it is well-centered. At that point, I peel back half of the batting, spray the wrong side of the batting, then smooth the sprayed half of the batting back over the backing. Doing it like this ensures you don't have to struggle with a sticky batting that is not centered on the backing. After the first half is done, do the other half of the batting. Add the top the same way, making sure it is smooth and centered on the rest of the sandwich. Then peel back half the top, spray the batting, and smooth the top back over.
I bought some really nice large clamps at the hardware store that I like to use on the layers when spray basting. Blue painter's tape comes in handy too, for keeping backing fabric from moving around while you are adding batting.
Final tip: Always spray from the outside of the quilt towards the center. This will minimize overspray.
Best of luck, and let us know how it goes!