The world of Gizmo is an ever evolving one, with new lands springing up from the nameless void, and new evils to be overcome accompanying them. We encourage people to get an immortal before building for Gizmo, as this gives them an opportunity to get a feel for the numbers behind the creatures they've battled with their mortals.
Once you've gotten an immortal, try to learn what the numbers mean. Relate them to how difficult a mobile is, and relate that to the quality of gear he should give out. This will help speed the area-approval process, and help you turn out excellent areas (Assuming, of course, that your descriptive skills are up to par).
Once you understand the statistics side of it, you have to build the aesthetic side of it. This means developing a story-line, a theme, and eventually mapping and writing out your area. Once you have the idea fairly well formed, with a general idea of difficulty for players and quality of equipment, you'll mail in a proposal, and, if approved, be assigned zone numbers.
An alternative to developing your own theme, is to find one elsewhere on the net. Many places have open areas, available for any who want them. With a few modifications, and editions to the stats to fit our curve, it will be ready to install on our very own Gizmo!
King Welmar's Castle is a zone we've made available so that people can see how things are structured. You can grab it HERE
By far the best way to write areas is in notepad. There is now an Online Guide to writing areas by hand, which is recommended to all, above using DikuEd or DikuWin. View it HERE You can also view it in plaintext format as well, HERE
If you want to jump right in Squirrel's DikuWin builder is ready for use. It was built with Gizmo specifically in mind. It is usable and intuitive. You can get it here. And view the project page here.
A third option is to use DikuEd. You can get the DOS and Windows version here. Or the UNIX version here. If you already have DikuEd, but it is configured for another Mud, you can download Gizmo's definition files here.
Good luck!