Hedam,
Gary McBride here. I wrote "Way of the Wicked" (and thanks to everyone for talking it up).
I have a few brief points of advice for evil campaigns:
1) We're in this together
In my experience, most players handle interparty conflict poorly, so find a way to either minimize it or at least control it. In an evil campaign, it's great to have a little back-biting and low-level scheming against one another. What's not good is guns-drawn, player vs. player combat. It's not conducive to campaign play and a great percentage of players taking killing their character very personally.
So, make the PCs part of an evil organization. Give them a boss (at least at first) who is watching them and will harshly punish killing one another. Have the PCs swear a blood oath to a demon lord, arch-devil, guild of assassins or evil overlord that they will work together. They don't have to like each other, but they do have to cooperate in their mission.
2) Evil is Active
Good can be reactive. Reactive evil, while theoretically possible, is almost always silly and pointless. Evil has to have a plan - some wicked scheme they are working towards.
Good guys can just wander from village to village saving random folks in distress. That works for team good guy.
Randomly murdering people is quickly boring. Team evil needs a plan that gets them out in the field roleplaying and interacting with allies and victims and the like. Fortunately there are lots of wicked schemes to choose from -- revenge, greed, lust for power, devotion to dark gods, teaching those fools at the ACADEMY WHO LAUGHED AT YOU THAT YOU ARE A GREATER GENIUS THAN THEY EVER WILL BE! *ahem* Sorry, got carried away there. You get the idea.
3) PG-13 Villainy
Graphic depictions of torture, sexual abuse and the like are always at unwelcome at the table. Yes, evil likely employs horrific methods. That doesn't mean you to describe them in details. Know when to employ the cut scene. Encourag villains to say things like...
"So, the paladin won't talk will he? I tie him down and introduce him to my minion Halthus the Flayer. 'Halthus has forgotten more about pain than you or I will ever know. You should feel fortunate. Tonight, you are going to experience a master at work. I would love to stay, but alas tonight I have other engagements. In the morning we'll talk. If you tell me everything you know, tonight could be your only night with dear Halthus. Hold out and I see you two spending a lot of time together.'"
...And then walk away. What ever you imagine happened that night, what did happen was far worse. Roll some dice, adjudicate the results and move on.
In "Way of the Wicked" you will find a longer exploration of what makes a fun evil campaign. This is just an introduction.
Hope that helps,
Gary McBride
Fire Mountain Games