I'd clean off all loose threads so that you don't get any loose threads caught between the top and batting (one gal calls them worms!), make sure the top is squared up and that seams that intersect the edges of the top are still intact. Then make sure backing and batting are about 3 or 4 inches bigger than the top on all sizes.
Other than that, check with the long-armer you'll be using and ask what he/she wants you to do - some want you to mark the center of all three layers, some may want you to pin the top edge of all three pieces together, some....well, the list goes on.
I've never stay stitched the edges before taking them for LA quilting since the stitching can inhibit the stretching that the LAer uses when the top is on the machine rollers.