We all know that it is going to take a white for Samsung to churn out the official Android 4.3 ROM. However, thanks to XDA, you can enjoy Android 4.3 on your Galaxy S4 right now. And since it is based on CM10.2 build, it looks very nexus like.
Download it from here and flash it using ODIN on your computer. To flash it, put your phone in download mode (volume down and power). Connect USB cable, and press volume up. Then use the ODIN and select the ROM file in PDA field and press the Start button. Wait for few minutes to download the ROM to your Galaxy S4 phone.
Just keep in mind that after installing the ROM, you will loose all data stored on it. So make sure to perform a back up.