Step 2: Step 2: Plan your layout
This step is also important for later steps. You will want to take some decent quality images of the area you are going to paint. Try to take them as straight on as possible. Also, you may want to clean the room first, as you can see in my photos, I didn't do this! Now, find a good image of what it is you want to turn the room into. Personally I used a SNES emulator on my PC and took screenshots of the features that I wanted in the room.
Now in photoshop or gimp or something similar, open both images. Using your room image as the base, remove the features that you want to add to your room from the other image and paste them into the room. Photoshop layers are wonderful for this. I created a layer for each item (Mario, Yoshi, coins, mushrooms....) and placed them around the room in a layout that flowed nicely. You can easily duplicate layers and move things around as you work in Photoshop. You may need to do some scale adjustments, be careful with this as you don't want to warp the dimensions of the item and make it look out of place. Take your time here and get what you want while you can change it easy. Be careful though, the more you get caried away, the more work you will have later on.
Once you are done here you should have a nice image of your room that you can print. Print this out the best you can. The larger the better. Also, be sure that your colors look right, this is your cheatsheet for the rest the project. Be sure to save this image for the next step as well.