This is the process I took the first time:
1. Make a backup just in case.
2. Flash bootanimation4u.zip from recovery (I use TWRP).
3. Reboot and install Boot Animations Root from the Play Store.
4. Go into the app's preferences and change install location to /system/media/ and leave the default filename (bootanimation.zip) and go back to the main screen.
5. Select any bootanimation from the Server tab and hit Install. (Tablet ones at the bottom of the list look best.)
6. Select the installed bootanimation again and hit Resize. Set it to 720x1280 30FPS.
7. Tap the options key and select "Preview current" Make sure you like it and reboot.
I use the Tablet - Shatter one, it looks like the one from the Jedi Roms, but higher quality.
If you Preview a few different ones and then decide to use one you downloaded earlier, delete it first then install and resize it again, or the preview will just be a black screen and might not work at all.
I believe you can preview before installing the animation if you buy the Pro version.
Check out a video tutorial here: Boot Animations
PLEASE NOTE I DO NOT HAVE THE PRO VERSION.
I have flashed through AGAT recovery and it said it has installed properly.....enjoy!
I then rebooted - nothing just a black screen w/ my custom boot sound.
Once I had booted I looked in /etc and sure enough there was a bootanimation.zip
Once I removed that, sure enough I had an animation.....NOT the Boost animation that came with my phone but a much older looking one (possibly Samsungs stock) It just says ANDROID with shiny letters.