I like to use the erase tool that blurs things, only I get far back from the line and click like a hundred times until it blends with the background just so. A lot really depends on the color of the background and if your image matches it or not. A straight white or black background is the hardest for me to blend with. Just something I picked up from years of trial and error lol. You know there are websites that have photo shop challenges and you can win stuff!? I just started looking into it myself this was my first submission ;)