One good way to get your feet wet in the world of sitcom writing is to write a spec script for an existing show. It should be a show that you are very familiar with, is currently airing, and is likely to continue airing for a few years. No agent or producer wants to see your spec script for Gilligan's Island, no matter how funny it is.

Here are a few things to take into consideration when developing a plot for your episode:

• Work within the limits of the show. Use existing sets and avoid location shots that would be expensive to shoot. Writing a spec script that uses an elaborate set, no matter how funny it is, will show the producers that you can't fit your ideas into the show's basic framework. If the show is animated, however, it's just as easy to draw any location, so go for it.

Does the sitcom of the future need to be 22 minutes and fit into a 30-minute timeframe? If someone was watching a show that was exclusively on the web, that might be too long. Maybe the perfect time for a “webisode” is 15 minutes, or 10, or even five.

• Don't introduce any new main characters. That's a decision for the producers and the head writer. Also avoid bringing in a character like a main lead's sister or father. It might not jive with the character's backstory. You can have a new secondary character in your script as long as he is out of the picture at the conclusion of the episode.

• Avoid any references to a continuing story line. Your episode must work by itself, even if the show has an ongoing story line. By the time someone reads it, that story line may have changed. Also, remember that the producers are the only ones who know what's in store for the characters.

• Don't rock the boat! If two characters on a show are involved in a “will they or won't they” romantic tension, you can't put them together. Those are major decisions made by the producers.

There are several alternatives to Final Draft, including other software and free applications that can be downloaded from the Internet. You can also find templates that can be used with almost any word processing program. But Final Draft is the industry standard, and it gets better with every new release. If you are serious about scriptwriting, it is worth the investment.

• Look online for sample scripts of the show to see how they are laid out. If you're using screenwriting software like Final Draft, you can download templates for pretty much every show on television.

• Watch out for character entrances and exits. You don't want someone in a scene standing around with nothing to do. Find funny ways to bring characters on and off.