But, I have my method...
The first thing I do is tack (yes tack!) the quilt top up on my design wall, so that the wrong side is facing out.
This particular quilt is about 72 inchs long by 60 inches wide. So because it is longer than I am tall, I put this one up so it is sideways. A smaller quilt I might do length wise. A larger quilt means moving some furniture.
Next, without pulling out the tacks I sort of hook the batting onto the tacks, in this case the batting is a thin poly so I snip a tiny hole to slip the tack through.
Now, as you can see, the batting hangs down and covers the whole top, so I know, I am not going to have a corner or edge that is a bit short -- though if you look closely, the quilt top is not completely covered in that bottom left corner -- easily fixed in next photo...
When you pull the batting out of its plastic bag, it is always somewhat scrunched up and wrinkledy and those wrinkles, if left could cause problems later, so I take my iron and fill it with water. I turn on the steam and without actually touching the batting hold the iron, with the thing steaming like crazy near to the quilt at a slight angle. If you hold it so the bottom is sideways, it won't seam, but at this bit of a dippy angle, the batting receives enough steam that the wrinkles relax. Works for cotton batting or the 80/20 type batting just as well... I think that I just might invest in one of those clothing steamers -- I'm thinking on it.
Now then, once the batting has been completely smoothed and is hanging straight, I PIN the backing onto the quilt top and batting -- no snipping holes to keep it in place. I only pin up at the top edge. No need yet to pin baste the whole thing (unless you plan to quilt from the back, then you can skip the next step.)
So, once I have good ole safety pins all along the top edge. I pull out the tacks from the wall, being careful not to drop the whole thing (though, I have without too much extra trouble.) and turn the three layers so that the quilt top is now facing outwards -- this is where a slightly taller husband or teenage son comes in very handy. They hold it while you retack that top edge back onto the wall. Just use enough tacks to keep it straight and not pulled in any one area. Smooth out the layers and start to pin or thread baste from near the top. Work your way down and across, by putting your arm underneath. Because you are letting gravity do the straightening for you, it is not a big headache having to smooth and re-smooth things.
Once you have safety pins placed every 4 inches or so all over the quilt, you can take it down and start quilting it.
I have been using this method for quite some time now (10 years at least) and very rarely do I have a fold over or a 'bump' show up on the back -- usually that will happen if there is something wrong with the piecing on the front!
Now, this particular quilt should have been done quite a while ago. I am teaching a class on how to do the top in October and I meant to have it ready to "advertise" the class, so now I HAVE to have it done by next Tuesday to show it so that someone, anyone will sign up for the class by mid October. It is almost like I sabotage myself! So, now that it is layered, I need to find the time to get it quilted... and very soon!
Note -- Yes, this does create alot of pin holes in your wall, so think ahead before you use my method. My particular reasoning is that at some later day, I can buy some polyfilla and fill those holes and paint the whole room. You have to polyfilla holes anyway before you paint so does it matter if there are a hundred holes or 10? Up to you to decide...