Myself, I have internal HDD, so everything will relate to that. If you have USB HDD, you must change path's accordingly.
What we need?
- FTP client (I used Total Commander);
- Avatar Friday Patcher (http://xbox360iso.com/showthread.php?t=347471);
- your profile XUID;
- some avatar DLC (http://xbox360iso.com/showthread.php?t=342145)
Ok, let's get to work.
1. Download avatar DLC
2. Unpack it to some directory (my example: G:/avatar_1/)
3. Create new directory for patched items (my example: G:/avatar_2/)
4. Start Avatar Friday Patcher
5. Type AAAAAAAA in New Tilte ID. This way, all our avatar files will be stored in one place on HDD.
6. Mark New XUID and type your XUID there (how to get your XUID -> use search on this forum).
7. Select input directory and find your directory with downloaded unpacked files (the one we created in point 2).
8. Press scan for files.
9. Select output directory (the one we created in point 3).

10. Press proceed and wait couple of seconds.
11. After receiving 'done processing' message, close Avatar Friday Patcher.
12. Connect to your X360 through FTP.
13. Go to 0:/Hdd1/Content/0000000000000000/
14. Create AAAAAAAA directory there (8 times letter A).
15. Enter that directory and create directory 00009000 there.
16. Copy files from avatar_2 directory into 0:/Hdd1/Content/0000000000000000/AAAAAAAA/00009000/

(obviously, you will have far less files on your xbox)
17. You can safely delete directories from your PC's HDD.
Voila! Everything should work like a charm. Go to your NXE and customize avatar with new stuff.
taken from www.xbox360iso.com
enjoy Fella
Console Guys