If it's small, I tape it to the kitchen counter & thread baste it (in that half zig zag pattern). If it's larger (crib size & up), I tape it to a smooth floor. Before I had a smooth floor (just a tiny galley kitchen & tinier bath, with carpeting everywhere else), I bought a piece of particle board with a laminate finish on it & would lay it on the carpeting when needed & tape to that.
I always tape down my backing. I get wrinkles otherwise. You just want to smooth it flat & then tape -- don't pull or you'll get dog ears for your quilt corners & anywhere else you tape. Masking tape works best; painter's tape is usually okay, too, but I had trouble with it a couple of times so I don't use the blue painter's tape anymore. Lay the batting, then the quilt top gently on top of the backing & smooth with your hand. Then, you want to draw an imaginary line down the middle vertically & horizontally. Start pinning in the center of your quilt & work your way out to the edge horizontally, then vertically, then fill in the rest of that quadrant working your way out from the center, gently smoothing any wrinkles toward the edge as you go. When you finish the first quadrant, go on to the next & repeat until finished. Those curved safety pins really made a difference for me.
I personally have found that when I pin all the way to the edge, my pins get stuck on my extension table, so I have started thread basting the edges of my quilts, rather than pinning them. I really love the results so much that I tried a small wall hanging with thread basting & think I may just switch over to that entirely. I can use straight pins to hold things in place while thread basting & it works great. So much easier to remove than safety pins.