Unless you're perfect, you need to rip out seams now and then. Here's a helpful way that will reduce your time a little.
From the BOBBIN side of your seam, rip out your stitches every 3-8, depending on how dense your stitches are. I usually go about every 5 stitches.
|first ripped stitch, heading to the right to finish|
Once you're ripped out your stitches, your seam will look like this:
|about every 3-4 stitches ripped; this seam is denser|
Turn over your fabric, so the NEEDLE side of your seam is facing up.
|see the loop to the right of the seam ripper?|
Starting at an edge, gently pull on a stitch. You should get a big loop. Pull on the loop gently and you should be able to pull a long thread. If you pull on the loop too much with the seam ripper, you'll rip the thread - pull with your fingers once you get it started.
You should end up with a long thread like this:
Clip your long thread and brush off/pick off your short threads and you're done. If your seam is really long, you might have to clip your long thread a few times to help it along. My seam here was only 1.5" long to rip out so my long thread came apart in one length.
What I like about ripping out seams this way is that it's less tedious than ripping every stitch and you don't distort your fabric by pulling it apart. If the sewing is really dense, it's never easy to pull out the stitches - take your time and you'll get better results.