Cutting Out Your Subject
The first thing tip for replacing a Background is to use a solid backdrop. Try to choose something similar to the Background you will then be placing your subject on since Color and Light will reflect (Ex: using a green backdrop will give a slightly green tint to the model).
For the sake of time I’ll use the Magnetic Lasso to select me out of the backdrop. It’s not going to be anywhere close to perfect, but once you have it selected you can convert that into a Layer Mask and select the areas you missed. The Lasso Tool isn’t perfect, so it’s almost always necessary to go back in and fix the areas you missed.
By bringing up the properties window you can lower the density slider which will allow you to see exactly which areas need to be added.
Once you are finished you can reduce the crisp line of the edge by going to Refine Edge. Since we’re going to be adding some Motion Blur and using the tiles I’m not going to be too particular about the edges being exactly perfect.