How to install a new ROM (for all except S-ON HTC devices)

People always ask me how to install a new Android ROM onto their devices. This is very simple and I'll try my best to make it simpler. This tutorial assumes that your devices is rooted and you have a custom recovery (like Clockworkmod, TWRP or 4ext recovery) installed.

Before we get started, here are a few things you need to know.

1. Installing a new ROM requires a factory reset of your device. This deletes everything except user data files. Things you lose include user apps, contacts, messages, call log and saved WiFi passwords. On the other hand Gallery, Music, Downloaded items and files you can see in your file manager are not lost.
2. If you are installing an upgrade of your previously installed ROM, data wipe is not mandatory, unless the developer says so. Nevertheless, a data wipe is always recommended.
3. To backup data, you can use different apps. The simplest one you can use is Super Backup. For advanced users, I'd recommend Titanium Backup. This data can be restored after installing the app once the ROM has installed.
4. AOSP ROMs (Cyanogenmod, Android Open Kang Project and Paranoid Android) mostly do not have Google Apps included due to copyright issues. Google Apps or gapps are therefore separately downloaded and installed as a zip. You can downloaded the latest gapps for you ROM from here.

Here is what you need:

1. A custom ROM zip (and gapps, if required).
2. A rooted device with a custom recovery installed. This includes all devices except S-ON HTC devices. S-OFF HTC devices can use this method. For S-ON devices or to check which one are you, click here.

Here is how you install a new ROM:

1. Transfer the ROM to your internal memory. Internal memory is preferred because it is safer than an SD card because of a risk of corruption.
2. Boot your phone into recovery. Every device has its own way to boot into recovery which you can easily find out by googling it. If you can't find it, ask me.
3. Once in recovery, select factory reset and confirm. Then wipe cache. Then go to advanced and wipe dalvik cache. This completes the wiping process.
4. Go back and select install zip. Select and install the custom ROM zip.
4a. Install the gapps zip, if applicable.
5. Reboot your device.

Congratulations, your new ROM is ready to use!

Applicable to (but not limited to):
1. All Samsung Galaxy S devices.
2. All Samsung Galaxy Note devices.
3. Virtually all Samsung Galaxy devices.
4. HTC Sensation (if S-OFF).
5. All Nexus devices.