Thanks to pankaj88

REQUIREMENTS:
- any file that you want to replace or add to your phone;
- an existing cwm flashable zip file to use as a base - I've attached one below;
- 7-zip;
- Notepad++.


STEPS:

DIRECTORY STRUCTURE:

(1) Download and place the sample.zip anywhere on your desktop;
(2) Right-click on it and choose: "7-Zip / Open archive" [*DO NOT extract; just *Open archive*];

Now you should see two folders: one called "system" and one called "META-INF".


I - FILES AND FOLDERS:


Let's start with the "system" one, so double-click on it:

In there, will go all files that what you want to add or replace to the system. So let's say for example that you want to replace the bootanimation and bootsound. To do so, we have to create sub-directories in the /system/ folder by following this easy method:

- On your desktop, right-click on an empty spot and select "New / Folder" then edit the name to "etc" (no " ") using no CAPS or space at the end;
- repeat the process to make another folder called "media";
- drag those two new empty folders into the /system/ folder of the 7-zip opened archive [just click yes on the popup dialogs];
- now simply drop the two files in their respective place: the sanim.zip file should go in '/system/media' folder and the PowerOn.wav into '/system/etc' folder.

.. If you have more files to add, just follow the logic above; I'm sure you get the idea by now..

/system/app - all the system apps (SystemUI.apk etc)
/system/framework/ -framework-res.apk, twframework-res.apk, android.policy.jar
/system/etc - vold.fstab, PowerOn.wav(bootsound)
/system/media - sanim.zip (bootanimation) (only for custom ROMs)
/system/lib - libraries (*.so)

II - UDATER-SCRIPT

The other folder included in the opened archive is named "META-INF" and all the file in it should be left unchanged.

That's it !!
Congratulations you've done your first CWM patch !!!

NOTE: Always backup your existing system file that you are going to replace by the patch(zip).