If you want to have the best experience on your Xperia Ray, I would ask you to downgrade to Gingerbread (Android 2.3) from ICS (Ice Cream Sandwich). I have tested ICS (Ice Cream Sandwich) on my device, and never found the desired experience. Select Gingerbread, it’s fast and that’s the sole reason for me sticking to Gingerbread over the ICS.

1. Download Flash tool from here  (go to installation tab). 
2. Download Android 2.3.4 – Build 4.0.2.A.0.42 from here or here1
3. Download Android 2.3.4 – Build 4.0.2.A.0.62 from here or here1

Procedure to Downgrade Sony Xperia Ray from ICS to Gingerbread;

1. Install Flashtool. The default installation location is (C:\Flashtool)
2. Also install the driver package found under ‘C:\Flashtool\drivers’ if you don’t have already (select pro-ray adb drivers, flash mode drivers and fastboot drivers).
3. Unzip the file downloaded at 2nd requirement and place it under ‘C:\Flashtool\firmwares’.
4. Open Flashtool, click Flash sign and select ‘Flashmode’ (see the screenshot above).
5. Select ST18i and click OK.
6. Follow on-screen instruction (unplug it from USB, power off, press volume- and not the back button, plug the USB cable) and you will have Gingerbread on the phone.

Root and Unlock Bootloader (Gingerbread only) of Sony Xperia Ray;

1. Download the zip file from here.
2. Connect Phone to USB (Make sure in settings, you have checked ‘Install unknown resources + USB debugging + Screen awake + activate Mass storage mode).
3. Execute “RUNME.bat” inside the folder you extracted at no 1.
4. Follow the instruction that is being displayed.
5. The phone will be rebooted and it’s bootloader unlocked and rooted.
   { if the doomlord script doesnt work at once then try flashtool root option too}
   check if your device has been rooted or not it via Root checker App

Install Busybox and CWM Recovery on Sony Ericsson Xperia Ray;

1. Install BusyBox Free from ST Ericsson from Google Play. Open it on your device and let it install few files.
2. Download the SE Tweak Installer from here (XDA forum page).
3. Connect Your Phone to USB
4. Run the SE Tweak Installer, select the device type to the Ray one (Make sure you have checked ‘Install unknown resources + USB debugging + Screen awake + activate Mass storage mode)
5. Press Install and follow the process.
6. Check Auto Reboot if you want to test right away (while reboot, press volume+ key multiple times.

Installation of Android 2.3.4 – Build 4.0.2.A.0.62 on Xperia Ray + Unlock Bootloader + CWM 

( After installing flashtool. go to c:/flashtool/drivers and install the drivers.exe. it will take time(3 Mins) please wait )

1. Unzip the file downloaded at 3rd requirement and place it under ‘C:\Flashtool\firmwares’.
2. Open Flash Tool
3. Click ‘Flash’ – the first icon
4. Select Flash Mode
5. Now select the firmware version 4.0.2.A.0.62. 
6. On Firmware content, make the selection as shown in the above screenshot (wipe data, cache, apps log and system only). See the exact selection shown in the screenshot.
7. Click ok, and if you have followed the steps correctly, you will have firmware 4.0.2.A.0.62 + unlocked bootloader + root + CWM

http://forum.xda-developers.com/showpost.php?p=14002417&postcount=1

How to remove apps (pre-installed apps)
http://androidflip.com/remove-pre-installed-android-apps/

Some Custom Rom (to increase performance)
http://forum.xda-developers.com/showthread.php?t=1905575

http://phones3xe.blogspot.in/2013/03/sony-xperia-ray-urushi-st18i-custom-rom.html