Use the lasso and remove as much as possible before you use the eraser or magic wand. Depending on how many colours are in your image, and the definition between foreground and background, you may be able to use the magic eraser, or the extraction tool. You can also mask the area you want to keep, and delete the rest. With the wand turn the tolerance down. there are a number of different ways of doing this. finding the one that works the best for you is the hard part.