[Sony Ericsson Xperia Neo, Pro] Jass5991:
Before I begin, Mods, PLEASE pin this. I (when I was a noob) had absolute difficulty installing ROMs. This is very noob-friendly, fixes Status 7 errors, and is easy to follow.

Alright friends and future flashers. I used to have difficulty installing ROMs. Now that I know how (after going through numerous tutorials), I'd like to make it easy for ALL of you. Enjoy your Custom ROM!

Before beginning, you need Android's SDK,Flashtool and The latest Official firmware.

If ever your phone needs to install drivers, let it install, don't unplug the phone or whatever.

And, battery at least 30%. Mine does it at even 20% without issues, but just to be safe.

Step 1: Revert to Stock

You don't need to downgrade. After flashing the latest stock kernel, I have flashed every single GB and ICS ROM in existence without issues, so you don't need to flash a specific one. But, latest one tends to be more stable. Here's what you do:

Get the latest Global ftf for your phone. Then, flash it using Flashtool. I won't go into specifics, but PM me if needed

By Now, you should have a stock EVERYTHING. Boot up the phone, run through the whole set up process. Once you are done, you need to get your IMEI number. Do this by following the steps here.

In the end, you should have the bootloader unlocked. If you come up with something like bootloader already unlocked, then you are good to go. Now onto......

Step 2: Preparing your Flash.

Download the ROM of your choice. I'd recommend FXP's Unofficial CyanogenMod9 as it has the best stability and no ICS Multitouch issues. If it is GB, any ROM will do. Most of them are stable.

Now, in the case of CyanogenMod, they often come with their own custom Kernel. It is in the zip file, known as boot.img, and you simply extract it to your platform-tools folder in the android-sdk folder you downloaded to unlock the bootloader. This is also true for some MIUI ROMs I've come across. Read their forum posts for more info on which kernel to use.

Copy the ZIP file to your sdcard. It does not have to be the root of SDcard, anywhere will do.

By the end, your Custom ROM's ZIP file will be in your SDCard, and the kernel file (a.k.a. boot.img or whatever_the _kernel_name_is.img) will be here:

32bit Windows: C:/Program Files/Android/android-sdk/platform-tools

64bit Windows: C:/Program Files(x86)/Android/android-sdk/platform-tools

Now we can

Step 3: Flash your Custom ROM

In the folder above (depending on OS version) press Shift+RightClick. Options will show up. Select "Open Command Prompt Here". A Command Prompt will open (duh).

Turn off your phone. Wait 10 seconds. While plugging in your phone, press the Menu button (the Right button). The LED Indicator should turn blue. This shows your in fastboot mode. If it starts to boot, rip out the battery and try again. DON'T STOP PRESSING UNTIL IT TURNS BLUE.

Now, type EXACTLY AS FOLLOWS, ONE AT A TIME. Just type in the lines with the "-" before it, but don't put in the "-" when typing it. The line underneath in brackets is an explanation, so you understand what is happening.

-fastboot devices

(This is actually a quick test I do to see if my phone is connected in flash mode or not. If nothing happens, it is not in flash mode or the drivers are installing)

-fastboot flash boot boot.img

(This is telling fastboot to FLASH the BOOT partition of your phone with the file specified. If you are using a different kernel, simply replace boot.img with the name of the kernel, ending with .img and wait for it to finish. Won't take long)

-fastboot reboot

(This causes the phone to reboot)

Now, while it is starting up, keep repeatedly pressing the Volume Down button until you are in ClockWorkMod Recovery (Assuming you are using it. CWM is the most popular and most kernels use it) Then, If you choose to, make a backup. I personally don't, as it is not too big an issue and I never revert to an old ROM anyway.

After that, choose Factory Reset. This will remove ALL data in your phone except your Stock ROM. Then, Clear Cache. You might've noticed it already did that when you Factory Reset, but this is for safety. Finally, in advanced, Wipe Dalvik-Cache and Wipe Battery Stats. I do this all the time for safety.

Now, the fun bit. GO to Install ZIP from SDCard. Select Choose ZIP, find your ROMs ZIP file, and install. It might take awhile, but not too long. Just be patient. When it finishes, flash anything else the ROMs forum post says to flash (Gapps, Patch, etc) and select Reboot Phone.

Step 4: Done!

Your phone will start up. First time is always slow, but this WILL WORK. Congratulations. You now have a Custom ROM

If you get a Status 7 error while flashing a ROM, reboot recovery and wipe everything again. If that doesn't work, flash official firmware and try again.

Credits to:

-Google: Providing Android SDK and Gapps

-Androxyde: Flashtool

-Madfysh: List of Official ICS ROMs

FXP: Creating CyanagonMod9

-And YOU!

P.S.: If you're confused, or feel this could use something extra PM me.