I feel your pain! This is why I choose a lot of scrappy type patterns.
I had a lot of problems with matching seams, too. You have received great advise. A couple of things that have helped me is to stitch at the seams. That's right. Don't take on the long seam, first stitch at every seam intersection. Then, you can sew the long seam. The other thing that helped me was to make sure my fabric is going in opposite directions. By this I mean that if your top fabric seam is facing towards your machine, the bottom fabric seam is facing away from it. This helps to match the seams. Several of the top quilters taught me to do it this way.
Good luck with your future quilts. I look forward to seeing what you do.