Link to original: http://sphynxcatvp.nocturna.org/articles/sc-empfilter.html
The first problem any unshielded empath notices is the overwhelming amount of impressions from other people. You don't know where "you" stop and "other people" begin, particularly when you've been around one or more people for a while. Confusion is common from having multiple emotions vying for attention, and most of them aren't yours.
The solution? Shields designed specifically to filter out the emotional excess that would otherwise overwhelm you.
Depending on your shielding skill and/or natural ability to "just do it", there will be varying degrees of difficulty associated with any of these. Just practice until it becomes second nature. There's plenty of methods. The thing to remember, though, is that they're merely visualizations that point you toward your goal, which is a state-of-mind that enables you to function in a situation that would otherwise be overwhelming.
If you've ever walked into the back of a bookstore from a crowded area, you should have noticed an immediate drop in noise level. My method is very much like that, imposing that sort of quiet in my mind. It doesn't filter out *everything* - just as if you're in the back of said bookstore, it doesn't block out ALL the noise, just a lot of it.
Other visualization methods include
A "sound filter" between you and the world, with slider switches that can adjust the noise level coming through - like an audio amplifier can adjust the amount of balance/treble/base on a stereo.
Plugging your mental ears with cotton balls, or burying yourself in a big pile of cotton or a fuzzy blanket.
Mentally close in on yourself, ignoring the rest of the world. Dive into your own thoughts, contemplate your navel if it helps. :) Imagine conversations with friends, compose a piece of text (story, LiveJournal post, etc.) in your mind, something to take the focus off the world and into yourself.
Visualize yourself in the background of your current location. Then start "fading out", until nearly transparent. Then let the thoughts, emotions, and general "bad vibes" pass through without tangible effect. You may feel more "detached" than usual from the current situation, so just be aware of that.
"Know Thyself" - Be sure what you're trying to block is genuinely not coming from yourself. Be sure your mind hasn't set up an "amplification loop" where it concentrates on a small tidbit of something in order to be able to figure out what it is.
Make sure your diet is good, that you're taking proper vitamins, and that you aren't being hit by medication side effects. Modify your diet and include more fruits and veggies, particularly if you're normally an example of the "fast food junkie" method of living. If you're a vegan, make sure you take plenty of b-vitamin supplements.
If necessary, leave. It may not be an easy decision, but you may need to leave the area in order to get yourself under control. Sometimes just "stepping outside for a minute" will do the trick, sometimes you need more time. It all depends on the situation.
If you need a longer break (Say, continued contact with friends is just getting to be too much), then just say that you need a little break from everyone else's problems for a while, and that you'll be back when you've gotten your head together.