I sometimes get in a hurry, and get a bit careless on my 1/4 seams, and I think that throws me off. Maybe that's part of it.

Great tips ... Tkx

If your seams aren't matching because the top fabric always seems to 'walk' a bit further than the bottom fabric, try pinning the center, pin the last edge, and piece with your walking foot.

Jan in VA

That's definitely part of it. If your seams are not all exactly the same, corners will not match. Consistency is extremely important. Eleanor Burns says you can fudge a little and ease or stretch the piece to fit. The other suggestions of locking seams and using a pin are very good. I use a pin when I am sewing triangles. I learned this from Fons and Porter.

Thats exactly what I do. Just learned that tip recently.

I like to butt the two seams together and use two pins, one on each side of the intersecting seam to really hold it in place and prevent any shifting. I find that using two pins makes a difference and I seldom have seams that do not match.

I use a tiny dot of white glue in the seamline instead of pins; helps me line up intersections better. To do this, use Elmer's white washable school glue and seal the seam closed with the heat from an iron. Just make sure the dot is tiny; it doesn't take much to "glue pin" a seam.

I always butt my seams, but, some days that isn't even enough. So rather than rip out the whole seam, I put a couple of stitches at the seams, check to make sure they are aligned and then sew the whole block. I have also tried pinning the seams, but had trouble doing that to. By just sewing a couple of stitches over the seam, the worst that happens is I rip out couple of stitches instead of the whole thing.

A good investment is fork pins. They are two pins that hold each side of the seam allowance. I love them, but they are expensive.

Reading these, I can still hear Eleanor Burns saying, "wiggle, wiggle, wiggle" as she would match up two pieces with seams pressed opposite. That was in the good ol' days when I could still get PBS, (sigh).