I find that the seam work takes some effort. I try to blend by cloning both sides to the center and then blending with a bigger brush in a wide circular motion across the area.
Another key is to crop the original into a panarama, pror to squaring it, which "seems to seam" :) better. The better you do the pana, the less area has to be blended. But each image is different and you have to go with the flow. Practice makes perfect, or better at least! ;)