First of all, if you want to choose this, you should know WHY.
Go thru the questions. Who, What, When, Where, and then WHY ARE YOU EVIL?
Generally, Evil characters are not meant to be played in groups. They are selfish, harmful, and typically ruin other people's fun. However, there are exceptions.
Lawful Evil presents a type of character that might get along with others in your party. They are the type that believe that they are doing the right thing, as long as they don't break the Law. Typically, they will attempt to get the laws changed to favor what they are trying to do.
There is a very strong case for PCs being Lawful Evil, if they punish people who break the Law. Many typical heroes can actually fit this bill if your perspective of them changes. Orphaned masked men in the dark utilizing vigilante justice are clear examples of blurred lines.
The real difference between lawful good, Lawful Evil, and Lawful Neutral comes from 2 primary sources. Motivation, and Satisfaction.
Lawful good characters follow the rules, and stop those that break them because it is right. They don't want to see people hurt, or want to make the world a better place. Typically a LG character likes clear lines. A bad guy, a good guy. Police officers are good examples of this. They willingly put themselves in harms way to help others. They do so by following the rules.
Lawful Neutral characters follow the rules to help themselves out. Politicians, Mercenaries, and Lawyers are good examples of LN. They will follow the rules, and will spin the rules to their own favor. Rarely do they do things for free, and typically, they don't want moral questions. When the job is done, they only want to protect themselves, and get paid.
Lawful Evil characters want what belongs to them. This can be anything. Many extremists fall into this category. Religious zealots, Tyrants, Corrupt cops, and Thieve's guilds typically fall into this category. They will do what they can to get ahead. If the rules don't match, they will look for ways to change them, or find an obscure rule to justify what they do.
MOST IMPORTANTLY: Evil characters do not see themselves as Evil. They see themselves as RIGHT.
If you want to play an evil character, you need JUSTIFICATION.
Let's look at an example.
A character that I am working on for myself is a dwarven cleric of death. I haven't chosen a name yet so we will call him Ted.
"Ted is a worshiper of Kelemvor, and treats the dead with respect, laying them to rest while ensuring they don't come back up. He is a Lawful Neutral character who works as a grave tender. He leads religious ceremonies, prays for the dead, and comforts those who lose someone. Everything changed when his village was attacked. No one was left alive, slaughtered in the streets. Rage filled Ted's eyes, as grief took over his heart. He believes in justice and what is right.
He decided that it was his job to avenge the death of his family and friends. And that they too, should join, granting them a chance at peace. Now he works as a necromancer. He only raises deceased members of his family, and fights only against the corruption that took their lives. "
You see, Ted has Motivation. He wants to avenge his family's death. Ted has Satisfaction from bringing down his enemies, and knowing that his family members get another chance at peace. He justifies his actions in these evil acts because he believes they are RIGHT.
Often a Lawful Evil character will see him or herself as the bearer of a great weight. Ted does this job because it is his job. If he did it so no one else would suffer, he would be Lawful Good. If he did it because he no longer felt safe, He might be Lawful Neutral.