First, unplug your device from any chargers or headphones.
Next, take off any cases.
Take a cloth (regular microfiber here), or washcloth, towel, etc.
If you have a water bottle, turn it to the MIST side. If you do not have a water bottle, slowly dab your cloth into a bowl of water. Do NOT dunk the towel.
Give the cloth about three good squirts, or dab it in water until it looks like the one above.
Scrunch or wring up the towel to get excess water out. Basically, you want the cloth DAMP, not soaked.
Now, wipe the back of your iOS device with the damp cloth. After about five strokes, use a dry part of your cloth and wipe the water off. Make sure the device is dry to the touch.
Your device should now be cooler! If you have to repeat any steps, go ahead and do that. It's very important to COMPLETELY dry your device off.
Use this method on the front screen to get rid of pesky fingerprints, crumbs, and other crusty unmentionables.
Note: Yes, you are probably thinking, "Why would I put water on my device?". But, I have used a damp cloth to clean my iPod touch for a while now, and no ill effects. Just remember DAMP, not soaked.