The first thing you have to remember when picking up a new identity (a secret identity) is that it is secret. You can't tell your friends. This is the biggest problem for so many people who want to pick up an alter ego. No matter how much you want to you can't tell your friends. It is a purpose defeating act! I reapeat, don't tell anyone!
The worst person you can tell is your significant other, my friends! He or she is the most likely person to rat you out. I mean, at first, it will be okay, they will feel honored to be in on this little secret, well, not so little. I mean, a second identity is pretty big. But if you were, say to break up with that significant other (no matter how much you're in love, it's always a possibility), they will use your alter ego against you and probably at a time that isn't very useful for whatever plans your other self is trying to accomplish. And let's not forget, there is the possibility that your other identity is going to want to get a girlfriend, or even get married. And this can't happen if your girlfriend or wife knows that you even have a secret identity.
So remember, rule number one: Your new identiy can have NO contact with your old life. It defeats the purpose!
Okay, now, that we have that established, you might be thinking about what sort of person your alter ego is. Well, it's up to you, but I would suggest trying out a totally different persona. If you're they shy quiet type in your primary life, go for the bold, brash and perhaps misguided type for your new secondary life. Next, name your alter ego. Go ahead. He or she will need a name. Here, you want to avoid the obvious pitfalls of generic names. Use names like John, Bob, or Matt very sparingly. Your new ego needs a name that will stick out. I mean, let's face it, if you're going through the trouble of starting a new identity, it probably wouldn't do to be a lame one. But then, you've gotta be careful about being too stupid about the name; avoid things like: Zaphina, Nick Danger, or Igor Petrovski (if you're obviously not Slavic). This part is particularly easy if you're making an alter ego because you have super powers and are thinking of taking up a life of crime or planning on being a super hero. Just come up with a name that's in line with your super powers. Check the internet and make sure that no two-bit Marvel superhero doesn't already have your name.
Your ego is going to need a backstory. He needs an origin. Parent's names, birthday, be familiar with his or her zodiac sign, favorite foods, likes, dislikes, aunts, uncles, grandparents. I mean, it's convenient if he was an orphan, but there aren't very many orphans who don't know at least a few of thier foster parents' names, you know? You can make this up on the fly, but if you're not very good at that sort of thing, then you're going to want to sit down and spend some time fleshing out his origins.
Next, official stuff: If you can get him or her a social security number and birth certificate, that's ideal, but most people simply don't have access to these sorts of things. For the most part, this stuff isn't really that necessary. Let's face it, if you're a superhero, people are going to know that you have another identity. And for the most part, alter egos are shed from time to time and will fade out of existence, once you go back to your primary life. Oh, and that reminds me, if your alter ego is going to be somewhat permanent, then you're going to want to make sure that he or she doesn't get too famous. If you haven't figured out why, then imagine this scenario: Your real life wife is watching T.V. at home and sees a movie preview as you walk into the room. Only the new action hero in the movie looks a lot like you. She turns around and says, "Wow, this new action hero, Din Weasel looks a lot like you honey...wait a minute....Hey! I thought you were visiting your mother with cancer! You were filming a movie and making millions of dollars! How come we live in this shitty trailer! What the fuck is going on here!" You can probably smooth that one over with a diamond ring and a new house (you can afford it), but now your alter ego is compromised. And that is very nearly a case of breaking rule number one!
Most people create alter egos for fun and enjoyment and sometimes to further other goals, like getting a novel published or some such thing. Superheroes and villains have the most obvious uses for them, but the average Joe could use one from time to time as well. Just remember these few simple tips and you'll be on your way to leading the double life in no time flat!