It is definitely easier to keep things lined up as one goes.

I have no idea how to square up something that got way off course while it was being made.

This is the way I was taught in my first quilt class and it works great for me too.

I square as I go as well. RARELY do I have problems after that. When adding borders, measure your quilt at the mid points both vertically as well as horizontally. Cut BOTH either side/top and bottom at the same time with the measurement of your mid points. Ease in as necessary. At that point, your quilt SHOULD be square and you should not have to re-square before adding your binding.

I have never found it necessary to square up my entire quilt. I measure the quilt top in the center and 1/4 in from each side. I take the average of those measurements and that is what I use for my border. I sew the side borders on first and then the top and bottom borders on next. This also works if you want to miter your corners of your border. Just take the measurement and make that what you sew to the quilt leaving extra on the ends for the miter. Lay the quilt on a flat surface to work out your miter. When I'm pinning the border on I divide the quilt into fourths and the border into fourths and match it up. Sometimes I have to do a bit of easing in with pins. I've never had a quilt that didn't lay straight and flat when I was done quilting and binding it using this method.

I use my husband's large metal T square and start in with the upper right corner to make sure that is square both ways. Usually I only have to do a very slight trim or none at all because I do square up my blocks as I go. Then I switch to my 6x36" ruler and using the outer edge of my 2nd to last border I line up my ruler to trim the outside border a slight bit, sometimes up to 1/4" to get rid of variations in the outside edge usually due to the machine quilting pulling a little at the edges. Now I just keep his T square in my sewing lab and he knows where to find it if he needs it.

there are several videos on you tube on how to square up a quilt. check them out, they are very helpful

I square everything up as I go and when quilted and ready for binding it is usually pretty square, if not I just trim where it needs it.

Squaring up is terrifies me. I'm always thinking -- what if I jerk a little and mess it up? I hate cutting into something I spent so many months working on. I solved the problem by having the long arm quilter do the squaring up. Saved me a lot of anxiety. Not a solution for those who quilt their own, I know.

Count me in as one of those who 'squares as I go' quilters. I make sure each segment is square before adding the next layer. I usually come out very very close to 'square' when it comes to the borders.

I try to make sure my rows are sewn together evenly - check by folding the quilt in half as I go is usually good enough.

On multiple borders or a medallion I do the measure top mid and bottom and cut the next border length to the average dimension.

To make sure my whole quilt top is square, I measure corner to corner in both directions. If corner to corner dimensions aren't the same, then I have to fiddle with it to adjust anything that got sewn a little crooked, or maybe just smooth it out a little better and starch, and then recheck cross wise, length wise, and kitty corner again.

Once the quilt is quilted, it is what it is and I don't mess with it. Maybe it might go out of whack because some bit is more heavily quilted? I know I started with good dimensions so I do no more than trimming off the excess, making sure my outside border width is consistent enough to give me my 1/4" seam with enough batting for a puffy binding.

I would always rather re-sew a bit here and there than cut. Cutting is not reversible! As the carpenter says when he cuts too short, put it on the board-stretcher! :)