This step can be a little tedious, but it’s something you can do much faster with practice! I promise.
Zoom in using CTRL + (plus) for Windows or CMD + (plus) for Mac. Use the lasso tool (found in the tool tray or with L on your keyboard) to trace the background. You can add to the selection by holding the shift key and remove from the selection by holding the alt key (Windows) or option key (Mac).
Try to make the selection as close as possible to the edge of the object without cutting into it. To make my project easier, I'm tracing the lizard and inverting the selection to select the background.
Note: You can use the + and - keys to zoom in and out of your project while using either of the lasso tools.
The edges of our selection—in my case lizard—will need to be refined to look convincing. Once your object is selected, click Select > Modify > Feather. A menu will pop open. I used a pixel density of 2 around the edges of the lizard but you can experiment to see what looks best for your image. This step stops the hard pixel effect on the edge of selected objects.