Making textures seamless doesn't go with just blending, or rotating, or whatever. Some will do but for the better textures you waste the whole texture. Use a program that has a tiling option (Wally), look at the seams, use offset on it and tweak those seams in other programs. It depends on the texture how you would fix those seams. Copy'n'pasting bricks if it's a brick texture can help, going over it with a smudge tool, repainting little parts, it's all up to you. After a while, you'll get some experience with it.
After all, I found texturing to be much more dependant on experience and tryal'n'error than mapping. It's no exact rules that make a texture look good. It's having a feeling for it I guess...