Move to either Los Angeles or Orlando. Nickelodeon has television studios in both locations. It's a must in order to perform on the shows of the station.
Get a headshot and resume that is fun, upbeat and thorough. Nickelodeon seeks professionals through reputable talent agencies. You have to market yourself as a professional in order to be taken seriously by the network.
Submit yourself to agencies. You can get a complete list of SAG franchised agencies for free through the Screen Actors Guild. If you are seeking something a bit more detailed and personable than simply a mailing list, get the book for managers, the book for agents and the book for casting directors published monthly by Samuel French. The monthly updates make data changes. The books include detailed information about the agencies, including email and phone numbers when applicable. It also states what type of look the agents may be seeking and if they will take on inexperienced talent.
Inform your agent of your passion for acting on Nickelodeon. According to the company itself, this is how they prefer to be notified. Your agent will be getting something called the "breakdowns," daily sheets sent to agents and managers revealing all the parts currently being cast.
Watch Nickelodeon regularly. In order to properly audition for shows, you should know the characters and basic premises of the shows you'll be aspiring to perform on. Knowing the show can also help you dress appropriately for the audition, and it will give you an upper hand.
Attend a live taping of the television show that you really connect with and think would be a good fit for your talents and look. This can give you a bird's eye view of how life is on the set for the actors. In order to do this, simply call Nickelodeon Studios to set it up. Call at least two weeks prior to the date you'd like to attend. Call the California location at (323) 468-5050. Call the Orlando studio at (407) 363-8500.
If you do not have an agent yet, submit your headshot through an entertainment lawyer to the casting director of the show you really want to be on. If you do have an agent, ask him to send the headshot. Follow up with your agent without being pushy if you think he may not be sending you out for what you truly want.
Contact Nickelodeon to find out the air dates for the show you performed in by calling (212) 258-7579.