Steps

1. First off, you want your work area completely covered with work related material (think organized mess but nothing too bad because that could land you in hot water itself), and it's always good to have multiple windows open on your computer, for "researching" or "networking" or whatever it is that your supposed to be at work doing. An open outlook with several unread "attn: marketing ideas" etc. isn't a bad idea.
2. Place a pencil or pen behind your ear to give off the impression that you are writing down so much important imformation that if it were possible, your right hand, itself, would be a writing instrument - and remember proper pencil placement - if your boss walks by your desk on the left hand side, place the pencil behind your left ear, or this effect is lost.
3. Take a lot of bathroom breaks - and sit down when possible. I know, I know, this sounds gross but I live to get paid to spend 40 minutes in the can reading the funnies.
4. Get up and go talk to one of your friends in a different department, but leave your workspace very "busy" looking. I always tell the person next to me that I am going to "double check something with someone from a different department" but what I'm really doing is providing myself with an excuse if my boss wonders where I was for an hour. "Oh, didn't Gina tell you? I wanted to double check and make sure both of our departments were on the same page about the new add campaign, I know it's an important issue and I would hate to have any mix-ups." Your boss will appreciate your ability to pay attention to details but what your really doing is... well, you know...
5. If your in sales or "telesales" or any type of job that requires you to make a quota on phone calls per day/week/month, call up dell/gateway/local computer shop and just let them put you on hold for 20 minutes before hanging up. You're eating up your time and on the computer that tracks call time it appears as if your busy pushing clients to buy. I usually browse video game message boards while I'm on hold because when my boss walks by "I'm on hold, I've been on the phone for 20 minutes with this guy and he had to run to the bathroom, I'm close to a sale".
6. Personally, I fake diabeties - specifically hypoglycemia (http://diabetes.niddk.nih.gov/dm/pubs/hypoglycemia/). This will allow you to leave work every 1 1/2 to 2 hours and go enjoy a snack downstairs. And whenever you feel like just being a flake, your "blood sugar is really low and you feel very tired and dizzy. You're trying to correct this problem but you have good days and bad." Nobody argues with this; it's golden, trust me. I cannot tell you how much time I've scammed by doing this. make sure you do your research, remember, it's not a lie if you believe it.

Tips

• Always, always have a back up.
• A lie is not a lie if you can provide specific details about the situation (ex: "Why wern't you at the employee picnic on saturday?" Bad answer: "My stomach hurt, I'm sorry." Good answer: "You know what, I'm sorry about missing that. What happened was I was eating some chicken from that new Chinese place down on [blank - again, do your homework] and I wasn't feeling very hot. I feel very bad about missing the outing, so how about letting me help with the planning for the next event?" (This shows that your a leader, and plus you can pick someplace that dosen't suck - like Vegas.) Besides, your boss will probably forget anyway and if you do get asked, you're "Too busy with the new sales reports."
• Bring in a co-worker who is equally as lazy or hates the company as much as you - he/she is your perfect alibi.

Warnings

• Don't get drunk at the bar and brag about how you cut corners at work to other people - they may be interviewing at your company soon or know someone there.
• Occasionally, do a little bit of work so they keep you on the payroll.
• Don't tell anyone you don't trust about your secrets of avoiding work!
• Limit the amout of time you call in sick - it detracts from your credibility.