Step 1: Draw the sun on the wall. For the round part you can trace this (for example round tray or a plate) or use a string with a pencil to create a nice round shape
Step 2: Tape off the sunbeams. Use masking tape or other tape that won't damage the wall. I did this in several stages because the rays were quite close together.
Step 3 - Once the sun rays are made with the tape, first paint over the tape with the color of the wall (in this case white). This way you make sure that all the parts where the tape is not 100% on the wall have the color of the wall. This way you create a very smooth result.
Step 4: After the underpaint (in this case white) is dry, paint the rays with the right color. Check carefully whether you need 1 or 2 layers to get a nice result in terms of color.
Step 5: Take off all the tape and add some more pieces if necessary.
In the photo you see the XL giraffes set.