[Android Q&A, Help & Troubleshooting] AayushPathak:
This is a tutorial for those who are new to android OS and rooted their phones early out of excitement (most of you might have done that :p ;)) of getting to flash new ROM's, kernels and blah.... There might be a few terminologies you don't understand. If that is the case please refer to the all time android dictionary by Diablo67: Android terms, slangs and definitions

I posted the tutorial on my blog too, but I think it will be much appreciated if I post it here too:

If your phone keeps rebooting

If you've flashed a ROM and your phone won't boot into the home screen, it's probably because you forgot to wipe your data and/or cache. It's trying to boot into the ROM, but some leftover data from your last ROM is causing it to error out, and it'll reboot itself over and over again. If your phone's eating a big bowl of boot loops, your first course of action should be to wipe its data and cache, which you can do from recovery mode. This method assumes you're using ClockworkMod Recovery, like the majority of Android users, but if your particular phone uses a different third-party recovery (like AmonRA), you should still be able to find these options in the interface. They might just be in a different place. To wipe your data and cache:

1.Power down your phone. Turn it back on and boot into Recovery mode. This is a bit different for every phone, so you'll have to Google how to do it for your specific model. Usually it involves holding down another button, like Volume Down, as you turn your phone on. HTC phones will have to then select "Recovery" from a menu, while other phones will boot directly into ClockworkMod. You'll know you're in ClockworkMod by the words "ClockworkMod Recovery" at the top of the screen.

2.Use your volume keys to navigate the menus, and your power button to select menu items. Scroll down to Advanced, and choose "Wipe Dalvik Cache". When that's finished, go back to the main screen and choose "Wipe Cache Partition". Lastly, head to "Wipe Data/Factory Reset". This will delete all your settings and apps, but you should still be using the correct ROM.

3.Reboot your phone.

If Your Phone Boots Straight Into Recovery: Flash a New ROM

If, when you boot up your phone, it goes straight into ClockworkMod, then there's likely an issue with the ROM you flashed. Note that some ROMs boot into recovery mode automatically after flashing, so reboot your phone once from recovery mode to make sure you're having a problem. HTC users: if you boot up your phone, it might go straight into the bootloader—check to see whether you can choose "Recovery" from the list before continuing to the next step. HTC phones usually don't boot straight into recovery.

In this case, you'll want to reflash the ROM from scratch. Try again with the ROM that messed up your phone, if you so choose, but if that doesn't work, try an entirely different ROM. The best way to do this is to download a ROM from somewhere on the net and putting it on your SD card. You'll need to take the SD card out of your phone, and you'll need an SD card reader that you can plug into your computer. Here's how it works:

Plug the SD card into your computer. Drag the ROM's ZIP file to your SD card, and wait for it to copy.

When it's done copying, eject the SD card and put it back in your phone. Reboot into Recovery mode. This is a bit different for every phone, so you'll have to Google how to do it for your specific model. Usually it involves holding down another button, like Volume Down, as you turn your phone on. HTC phones will have to then select "Recovery" from a menu, while other phones will boot directly into ClockworkMod. You'll know you're in ClockworkMod by the words "ClockworkMod Recovery" at the top of the screen.

Use your volume keys to navigate the menus, and your power button to select menu items. Scroll down to "Install ZIP From SD Card" and navigate to the ZIP file you just copied over. Give it time to flash the ROM.

When it's done, reboot your phone.

Hopefully, your phone should successfully boot into the new ROM. From there, you can probably assume that the previous ROM that messed up your phone isn't going to work, and you'll have to find another ROM for now—or find another copy of that ROM that isn't corrupted. Remember to make backups of your working ROMs so you don't lose all your data!

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