1. Rename old Interface and WTF Folder to something else or delete.
2. Forget any 1.11, 1.15 or whatever versions. They're all out of date.
3. DL
MazzleUI Core V. 1.18_ docevl and extract to your desktop or whatever. You'll receive a directory named "MazzleUI-Core-1.18" with two folders named "Interface" and "Fonts" inside. Copy both folders into your
World of Warcraft directory.
4. DL
AddonPack V. 1.31 by docevl and extract into your
World of Warcraft/Interface/AddOns directory.
5. Login, make sure 'Load out of date addons' is checked.
6. Ingame, first of all adjust Video settings to your needs. UI will probably reload after that.
7. Go through Mazzifyer, answer all questions, don't forget to scroll down on all pages.
8. Have fun