Reserve a space far forward in the magazine's pagination scheme. Preferably the space should be a vertical one-third page or one-half page, and on the gutter. This space will be where the masthead will appear.
Make a list of staff members to include in the masthead. This list will largely depend on the size of your magazine's staff and the space available, but the masthead should always include the editor-in-chief, managing editor, art director and any designers who worked on the layout or cover. Some magazines list the "publishing side" along with the editorial staff, but it is not uncommon for the publishing staff and sales staff to have their own, separate masthead. When the two groups are merged, the publisher's name might appear higher than the editor-in-chief's -- especially if the publisher happens also to be the majority owner.
Open your design program and start a new page. The masthead should take up one column of the page, about 1/3rd of the space, in a typical three-column format.
Add each person's title to this column, with a few spaces between each. Write them in all capital letters so that they stand out as titles, in contrast to the persons' names that will appear beneath each title. The title-and-name listings should be stacked in hierarchical order: begin with the editor-in-chief and work your way down.
Type the name of each person beneath that person's title. The font size and type should be small enough so that each name fits on one line, i.e., without any line breaks.
Experiment to find the best layout for your particular magazine. You may be able to use the page differently. For example, some magazines use a full page masthead to include all staff members, while some use a horizontal row instead of a vertical column.