Here is a very quick tutorial about making a quilt sandwich–which can be super satisfying. First it is essential to clear a large space to spread out. Spread your quilt back, right side down, on the floor. Tape the edges (I use blue painter’s tape) to the floor so the fabric is smooth, but not taut. Pull off any stray threads.
Next unfold your batting and, starting from the center, gently smooth out any wrinkles. The batting sticks to the fabric so you may need to lift the batting gently to smooth out some wrinkles. Once your batting is nice and smooth, trim any excess that extends beyond the edges of the backing.
Then, lay your quilt top, right side up, on top of the batting. Your quilt top will be smaller than the backing and batting so you should be able to position it neatly. Again, starting in the center, smooth your quilt top onto the batting gently pushing any wrinkles to the edges. Finally, you can either baste or pin your sandwich together. I prefer pins because I find pinning (with curved quilting safety pins) keeps my sandwich smooth. It is also faster than basting. Sometimes I baste the pinned quilt after I take it off the floor. The basting makes it easier when you are doing the quilting. Here is my quilt–all sandwiched together and ready to go.
homemadecity.com 
This is so helpful! Thanks, B. The photos are great–very instructive for those of us who are terrified of taking the next step in their first-ever quilt project. One Q: why is the backing and batting larger than the front? Obviously it would be bad not to have enough–is this why? Do you end up trimming it later?
Funny you ask. The reason is so that you can position the top evenly. If the top is bigger than the back–1) you would have to trim away your top to get an even edge and 2) you can’t see where the edges of the back are. It is funny because I did not do this correctly for this quilt (grr!). Somehow my top was wider than the back. I blame math fatigue—I think I just measured wrong. Since this is a picnic quilt I didn’t really care about the finished dimensions. If it had been for a bed I would have had to add some fabric to the back. Once your sandwich is complete, you square up and trim away the excess batting and backing. As a general rule your backing should have an extra five inches all around. And I guess I should add, measure everything twice.
One more thought, I think the kosher thing to do is to trim the excess after you have quilted, but I find that creates a lot of unnecessary fluff in my machine. I guess if you trim after quilting, you might get a neater edge?