you must have these things in order to do this:
1. an Xbox 360 of course
2. USB drive (I recommend a 32GB USB)
3. A computer/laptop
4. an internet connection (for the computer/laptop)
THESE ARE A FEW THINGS YOU MUST KEEP IN MIND BEFORE DOING THIS:
1. DO NOT RUN THE EXPLOIT BEFORE DISCONNECTING YOUR CONSOLE FROM THE INTERNET, THIS COULD LEAD TO A CONSOLE BAN
2. DO NOT CONNECT TO XBOX LIVE WHILE IT IS IN THE MODDED STATE WITH YOUR MAIN ACCOUNT, STEALTH SERVERS ONLY LOWER THE LIKELYHOOD OF YOU GETTING BANNED AND YOU SHOULD NOT RISK YOUR MAIN ACCOUNT AND USE A THROWAWAY ACCOUNT INSTEAD OR JUST DON'T CONNECT TO XBOX LIVE
3. DO NOT MESS ABOUT WITH THE FILES IN THE FLASH, THIS CAN VERY EASILY BRICK YOUR CONSOLE
4. DO NOT RUN HOMEBREW USING YOUR MAIN XBOX LIVE ACCOUNT, IF YOU DO YOU WILL HAVE TO DELETE YOUR PROFILE FROM THE CONSOLE AND HAVE TO SIGN BACK (OR DON'T) OR ELSE YOU WILL GET BANNED FROM XBOX LIVE
the first thing you want to do is disconnect your xbox 360 from the internet, you will need to first go to the settings tab and press A on system
next you want to go onto network settings
and then hover over the network you are connected to and press Y to disconnect from it
(if you already formatted your usb through the xbox 360 you can skip this) grab your USB drive and plug it into your xbox 360
then go to storage
then select your USB drive
then you want to select format and then select yes on the pop-up then remove the USB drive
the next the thing you need to do is download a couple things, you need to download these:
Bad Update 1.3
XeUnshackle
XEXMenu 1.1 (CHOOSE XEX NOT ISO)
WinRAR (needed to extract XEXmenu)
Rock Band Blitz Trial
you will have 4 folders, right click them and hover over winrar then select extract here
once they are extracted the folders should look something like this, you then want to plug in your USB drive to your computer/laptop and copy the content folder to the USB drive
then open the rock band blitz folder and then you want to copy the files from this folder into the USB drive
then you want to open the XeUnshackle folder and copy everything into the USB drive,
if it tells you there is already a file with a certain name like default.xex click replace the file in the destination
in the XEXMenu folder you want to right click XEXMenu_v1.1-LIVE.rar then hover over WinRAR then click extract here,
then you want to right click the folder C0DE9999 and select copy,
then go into your USB drive, then content (if the content folder isn't visible then click view then show then click hidden items and then you should see the content folder) then 0000000000000000 and then right click and paste the folder
take out your USB drive from your computer/laptop and plug it into your xbox 360, then turn on the console and log into your profile
then go to the games page and then you will see Rock Band Blitz, start the game
when you press A on the title screen it may ask you what storage device you want to use, select the USB drive and then the exploit will start running
once the exploit has been successful you should see this screen, press X then press Y (you only need to do this once) and then press select to go to your dashboard and you should now be able to run homebrew and whatever you want
please note you will have to rerun the exploit every time you want to use homebrew and whatever requires a modded xbox 360